Amino acid sequences targeting human cd4, cxcr4, ccr5, tlr4, alphav integrin, beta3-integrin, beta1-integrin, human alpha2-integrin, cd81, sr-bi, claudin-1, claudin-6 and claudin-9, respectively, and neutralizing viral entry

ABSTRACT

The present invention relates to amino acid sequences that are directed against (as defined herein) human cellular receptors for viruses and/or bacteria such as e.g. Nanobodies specifically recognizing hCD4, hCXCR4, hCCR5. hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-B1, hClaudin-1, hClaudin-6 and hClaudin-9, as well as to compounds or constructs, and in particular proteins and polypeptides, that comprise or essentially consist of one or more such amino acid sequences. Said amino acid sequences may be used to prevent human cell entry of HIV, HCV, adenoviruses, hantavirus, herpesvirus, echo-virus 1 and others.

The present invention relates to amino acid sequences that are directed against (as defined herein) human cellular receptors for viruses and/or bacteria such as e.g. Nanobodies specifically recognizing hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9, as well as to compounds or constructs, and in particular proteins and polypeptides, that comprise or essentially consist of one or more such amino acid, sequences (also referred to herein as “amino acid sequences of the invention”, “compounds of the invention”, and “polypeptides of the invention”, respectively). Said amino acid sequences may be used to prevent human cell entry of HIV, HCV, adenoviruses, hantavirus, herpesvirus, echo-virus 1 and others.

The invention also relates to nucleic acids encoding such amino acid sequences and polypeptides (also referred to herein as “nucleic acids of the invention” or “nucleotide sequences of the invention”); to methods for preparing such amino acid sequences and polypeptides; to host cells expressing or capable of expressing such amino acid sequences or polypeptides; to compositions, and in particular to pharmaceutical compositions, that comprise such amino acid sequences, polypeptides, nucleic acids and/or host cells; and to uses of such amino acid sequences or polypeptides, nucleic acids, host cells and/or compositions, in particular for prophylactic, therapeutic or diagnostic purposes, such as the prophylactic, therapeutic or diagnostic purposes mentioned herein.

Other aspects, embodiments, advantages and applications of the invention will become clear from the further description herein.

When searching for their favorite host tissues, animal viruses and bacteria frequently attach to cell-surface receptors that have key roles in normal cell physiology. The receptors mentioned herein are examples of physiologically important receptors that have been usurped by nonenveloped and enveloped viruses for attachment, virus-cell fusion and/or virus entry into mammalian cell or partial virus entry into mammalian cell.

The polypeptides and compositions of the present invention can generally be used to modulate, and in particular inhibit and/or prevent attachment, virus/bacterium-cell fusion and/or virus/bacterium entry into mammalian cell or partial virus/bacterium entry into mammalian cell.

As such, the polypeptides and compositions of the present invention can be used for the prevention and treatment (as defined herein) of viruses and/or bacteria induced diseases and disorders. Generally, “viruses and/or bacteria induced diseases and disorders” can be defined as diseases and disorders that can be prevented and/or treated, respectively, by suitably administering to a subject in need thereof (i.e. having the disease or disorder or at least one symptom thereof and/or at risk of attracting or developing the disease or disorder) of either a polypeptide or composition of the invention (and in particular, of a pharmaceutically active amount thereof). Examples of such viruses and/or bacteria induced diseases and disorders will be clear to the skilled person based on the disclosure herein.

Thus, without being limited thereto, the amino acid sequences and polypeptides of the invention can for example be used to prevent and/or to treat all diseases and disorders that are currently being prevented or treated with active principles that can modulate virus/bacterium attachment, virus/bacterium-cell fusion and/or virus/bacterium entry into mammalian cell or partial virus/bacterium entry into mammalian cell. It is also envisaged that the polypeptides of the invention can be used to prevent and/or to treat all diseases and disorders for which treatment with such active principles is currently being developed, has been proposed, or will be proposed or developed in future. In addition, it is envisaged that, because of their favourable properties as further described herein, the polypeptides of the present invention may be used for the prevention and treatment of other diseases and disorders than those for which these known active principles are being used or will be proposed or developed; and/or that the polypeptides of the present invention may provide new methods and regimens for treating the diseases and disorders described herein.

Generally, it is an object of the invention to provide pharmacologically active agents, as well as compositions comprising the same, that can be used in the diagnosis, prevention and/or treatment of viruses and/or bacteria induced diseases and disorders and of the further diseases and disorders mentioned herein; and to provide methods for the diagnosis, prevention and/or treatment of such diseases and disorders that involve the administration and/or use of such agents and compositions.

In particular, it is an object of the invention to provide such pharmacologically active agents, compositions and/or methods that have certain advantages compared to the agents, compositions and/or methods that are currently used and/or known in the art. These advantages will become clear from the further description below.

More in particular, it is an object of the invention to provide therapeutic proteins that can be used as pharmacologically active agents, as well as compositions comprising the same, for the diagnosis, prevention and/or treatment of viruses and/or bacteria induced diseases and disorders and of the further diseases and disorders mentioned herein; and to provide methods for the diagnosis, prevention and/or treatment of such diseases and disorders that involve the administration and/or the use of such therapeutic proteins and compositions.

Accordingly, it is a specific object of the present invention to provide amino acid sequences that are directed against (as defined herein) human cellular receptors for viruses and/or bacteria such as e.g. Nanobodies specifically recognizing hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9 (also referred to herein as “Targets of the invention” or each of these referred to as “one of the Targets of the invention” or “Target of the invention”), in particular against Targets of the invention from a warm-blooded animal, more in particular against Targets of the invention from a mammal, and especially against human Targets of the invention; and to provide proteins and polypeptides comprising or essentially consisting of at least one such amino acid sequence.

In particular, it is a specific object of the present invention to provide such amino acid sequences and such proteins and/or polypeptides that are suitable for prophylactic, therapeutic and/or diagnostic use in a warm-blooded animal, and in particular in a mammal, and more in particular in a human being.

More in particular, it is a specific object of the present invention to provide such amino acid sequences and such proteins and/or polypeptides that can be used for the prevention, treatment, alleviation and/or diagnosis of one or more diseases, disorders or conditions associated with Targets of the invention and/or mediated by Targets of the invention (such as the diseases, disorders and conditions mentioned herein) in a warm-blooded animal, in particular in a mammal, and more in particular in a human being.

It is also a specific object of the invention to provide such amino acid sequences and such proteins and/or polypeptides that can be used in the preparation of pharmaceutical or veterinary compositions for the prevention and/or treatment of one or more diseases, disorders or conditions associated with and/or mediated by Targets of the invention (such as the diseases, disorders and conditions mentioned herein) in a warm-blooded animal, in particular in a mammal, and more in particular in a human being.

In the invention, generally, these objects are achieved by the use of the amino acid sequences, proteins, polypeptides and compositions that are described herein.

In general, the invention provides amino acid sequences that are directed against (as defined herein) and/or can specifically bind (as defined herein) to Targets of the invention; as well as compounds and constructs, and in particular proteins and polypeptides, that comprise at least one such amino acid sequence.

More in particular, the invention provides amino acid sequences that can bind to Targets of the invention with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein; as well as compounds and constructs, and in particular proteins and polypeptides, that comprise at least one such amino acid sequence.

In particular, amino acid sequences and polypeptides of the invention are preferably such that they:

-   -   bind to Targets of the invention with a dissociation constant         (K_(D)) of 10⁻⁵ to 10⁻¹² moles/liter or less, and preferably         10⁻⁷ to 10⁻¹² moles/liter or less and more preferably 10⁻⁸ to         10⁻¹² moles/liter (i.e. with an association constant (K_(A)) of         10⁵ to 10¹² liter/moles or more, and preferably 10⁷ to 10¹²         liter/moles or more and more preferably 10⁸ to 10¹²         liter/moles);         and/or such that they:     -   bind to Targets of the invention with a k_(on)-rate of between         10² M⁻¹s⁻¹ to about 10⁷ M⁻¹ s⁻¹, preferably between 10³ M⁻¹s⁻¹         and 10⁷ M⁻¹s⁻¹, more preferably between 10⁴ M⁻¹s⁻¹ and 10⁷         M⁻¹s⁻¹, such as between 10⁵ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹;         and/or such that they:     -   bind to Targets of the invention with a k_(off) rate between 1         s⁻¹ (t_(1/2)=0.69 s) and 10⁻⁶ s⁻¹ (providing a near irreversible         complex with a t_(1/2) of multiple days), preferably between         10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more preferably between 10⁻³ s⁻¹ and 10⁻⁶         s⁻¹, such as between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹.

Preferably, a monovalent amino acid sequence of the invention (or a polypeptide that contains only one amino acid sequence of the invention) is preferably such that it will bind to Targets of the invention with an affinity less than 500 nM, preferably less than 200 nM, more preferably less than 10 nM, such as less than 500 pM.

Some preferred IC50 values for binding of the amino acid sequences or polypeptides of the invention to Targets of the invention will become clear from the further description and examples herein.

For binding to Targets of the invention, an amino acid sequence of the invention will usually contain within its amino acid sequence one or more amino acid residues or one or more stretches of amino acid residues (i.e. with each “stretch” comprising two or amino acid residues that are adjacent to each other or in close proximity to each other, i.e. in the primary or tertiary structure of the amino acid sequence) via which the amino acid sequence of the invention can bind to Targets of the invention, which amino acid residues or stretches of amino acid residues thus form the “site” for binding to Targets of the invention (also referred to herein as the “antigen binding site”).

The amino acid sequences provided by the invention are preferably in essentially isolated form (as defined herein), or form part of a protein or polypeptide of the invention (as defined herein), which may comprise or essentially consist of one or more amino acid sequences of the invention and which may optionally further comprise one or more further amino acid sequences (all optionally linked via one or more suitable linkers). For example, and without limitation, the one or more amino acid sequences of the invention may be used as a binding unit in such a protein or polypeptide, which may optionally contain one or more further amino acid sequences that can serve as a binding unit (i.e. against one or more other targets than Targets of the invention), so as to provide a monovalent, multivalent or multispecific polypeptide of the invention, respectively, all as described herein. Such a protein or polypeptide may also be in essentially isolated form (as defined herein).

The amino acid sequences and polypeptides of the invention as such preferably essentially consist of a single amino acid chain that is not linked via disulphide bridges to any other amino acid sequence or chain (but that may or may not contain one or more intramolecular disulphide bridges. For example, it is known that Nanobodies—as described herein—may sometimes contain a disulphide bridge between CDR3 and CDR1 or FR2). However, it should be noted that one or more amino acid sequences of the invention may be linked to each other and/or to other amino acid sequences (e.g. via disulphide bridges) to provide peptide constructs that may also be useful in the invention (for example Fab′ fragments, F(ab′)₂ fragments, ScFv constructs, “diabodies” and other multispecific constructs. Reference is for example made to the review by Holliger and Hudson, Nat Biotechnol. 2005 September; 23(9):1126-36).

Generally, when an amino acid sequence of the invention (or a compound, construct or polypeptide comprising the same) is intended for administration to a subject (for example for therapeutic and/or diagnostic purposes as described herein), it is preferably either an amino acid sequence that does not occur naturally in said subject; or, when it does occur naturally in said subject, in essentially isolated form (as defined herein).

It will also be clear to the skilled person that for pharmaceutical use, the amino acid sequences of the invention (as well as compounds, constructs and polypeptides comprising the same) are preferably directed against human Targets of the invention; whereas for veterinary purposes, the amino acid sequences and polypeptides of the invention are preferably directed against Targets of the invention from the species to be treated, or at least cross-reactive with Targets of the invention from the species to be treated.

Furthermore, an amino acid sequence of the invention may optionally, and in addition to the at least one binding site for binding against Targets of the invention, contain one or more further binding sites for binding against other antigens, proteins or targets. The efficacy of the amino acid sequences and polypeptides of the invention, and of compositions comprising the same, can be tested using any suitable in vitro assay, cell-based assay, in vivo assay and/or animal model known per se, or any combination thereof, depending on the specific disease or disorder involved. Suitable assays and animal models will be clear to the skilled person, and for example include the expression of the receptors in Xenopus oocytes, after which the coupling of many Targets of the invention to ion channels allows the activation or inhibition of these Targets of the invention to be monitored in oocytes via voltage clamping techniques. Heterologous Targets of the invention can be functionally expressed in the oocyte by injecting exogenous, Targets-encoding mRNA into the oocyte and then allowing the oocyte's endogenous cellular machinery to translate and insert the receptors into the plasma membrane (see, e.g., Houamed et al., Science 252:1318-21, 1991; Dahmen et al., J. Neurochem. 58:1176-79, 1992). Following functional expression of receptors, the ability of ligands to induce transmembrane conductance changes can be observed via a two-electrode voltage clamp system (Dahmen et al., supra), which can detect either a depolarization or hyperpolarization of the membrane potential. Other suitable assays are e.g. described in the example section.

Also, according to the invention, amino acid sequences and polypeptides that are directed against Targets of the invention from a first species of warm-blooded animal may or may not show cross-reactivity with Targets of the invention from one or more other species of warm-blooded animal. For example, amino acid sequences and polypeptides directed against human Targets of the invention may or may not show cross reactivity with Targets of the invention from one or more other species of primates (such as, without limitation, monkeys from the genus Macaca (such as, and in particular, cynomolgus monkeys (Macaca fascicularis) and/or rhesus monkeys (Macaca mulatta)) and baboon (Papio ursinus)) and/or with Targets of the invention from one or more species of animals that are often used in animal models for diseases (for example mouse, rat, rabbit, pig or dog), and in particular in animal models for diseases and disorders associated with Targets of the invention (such as the species and animal models mentioned herein). In this respect, it will be clear to the skilled person that such cross-reactivity, when present, may have advantages from a drug development point of view, since it allows the amino acid sequences and polypeptides against human Targets of the invention to be tested in such disease models.

More generally, amino acid sequences and polypeptides of the invention that are cross-reactive with Targets of the invention from multiple species of mammal will usually be advantageous for use in veterinary applications, since it will allow the same amino acid sequence or polypeptide to be used across multiple species. Thus, it is also encompassed within the scope of the invention that amino acid sequences and polypeptides directed against Targets of the invention from one species of animal (such as amino acid sequences and polypeptides against human Targets of the invention) can be used in the treatment of another species of animal, as long as the use of the amino acid sequences and/or polypeptides provide the desired effects in the species to be treated.

The present invention is in its broadest sense also not particularly limited to or defined by a specific antigenic determinant, epitope, part, domain, subunit or confirmation (where applicable) of Targets of the invention against which the amino acid sequences and polypeptides of the invention are directed. For example, amino acid sequences of the invention may be raised by suitably immunizing a mammal (such as a Camelid) with Targets of the invention that have been expressed in a suitable expression system or that has been isolated from a suitable cell or cell fraction. In particular, amino acid, sequences of the invention may be raised against Targets of the invention (or suitable parts or fragments thereof) that have been refolded (for example using the techniques described in the review by Kiefer, Biochim. Biophys. Acta, 1610 (2003), 57-62), and amino acid sequences, Nanobodies and polypeptides that are directed against and/or that have been raised against a refolded Target of the invention form a further aspect of the invention.

The amino acid sequences and polypeptides of the invention may generally be directed against any desired Target of the invention, and may in particular be directed against Targets of the invention that have at least one extracellular loop or domain. Examples of such Targets of the invention will be clear to the skilled person based on the prior art cited herein.

According to a specific aspect of the invention, an amino acid sequence or polypeptide of the invention may be directed against (as defined herein) the Targets of the invention that are expressed on the surface of a cell and/or against at least one extracellular region, domain, loop or other extracellular epitope of one of the Targets of the invention. For example, such amino acid sequences may be raised by suitably immunizing a mammal (such as a Camelid) with a cell or cell fraction that has one of the Targets of the invention expressed.

In particular, according to this aspect, an amino acid sequence or polypeptide of the invention is directed against (as defined herein) at least one extracellular region, domain, loop or other extracellular epitope of one of the Targets of the invention, e.g. hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9, and is preferably further such that said amino acid sequence or polypeptide of the invention is capable of modulating (as defined herein) said Target of the invention, e.g. hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9. More in particular, according to this aspect, an amino acid sequence or polypeptide of the invention is directed against (as defined herein) at least one extracellular region, domain, loop or other extracellular epitope of a Target of the invention, e.g. hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9; and is preferably further such that said amino acid sequence or polypeptide of the invention is capable of (fully or partially) blocking said Targets of the invention, e.g. hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9.

According to this aspect of the invention, the amino acid sequence or polypeptide of the invention may be directed against any suitable extracellular part, region, domain, loop or other extracellular epitope of one of the Targets of the invention, e.g. hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9, but is preferably directed against one of the extracellular parts of the transmembrane domains or more preferably against one of the extracellular loops that link the transmembrane domains.

The amino acid sequence of such suitable extracellular parts, regions, domains, loops or epitopes may be derived by Kyte-Doolittle analysis of the amino acid sequence of the pertinent Target of the invention, e.g. hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9; by aligning the Targets of the invention belonging to the same (sub)families and identifying the various transmembrane domains and extracellular parts, regions, domain or loops; by TMAP-analysis; or by any suitable combination thereof. The invention also relates to amino acid sequences and polypeptides (as further defined herein) that are directed against and/or have been raised against such extracellular parts, regions, domains, loops or epitopes (and/or that are directed against and/or have been raised against suitable parts or fragments of such extracellular parts, regions, domains, loops or epitopes and/or against synthetic or semi-synthetic peptides that are derived from or based on such extracellular parts, regions, domains, loops or epitopes).

In particular, amino acid sequences and polypeptides of the invention are preferably such that they:

-   -   bind to an extracellular part, region, domain, loop or other         extracellular epitope of one of the Targets of the invention (as         described herein) or against a peptide derived therefrom with a         dissociation constant (K_(D)) of 10⁻⁵ to 10⁻¹² moles/liter or         less, and preferably 10⁻⁷ to 10⁻¹² moles/liter or less and more         preferably 10⁻⁸ to 10⁻¹² moles/liter (i.e. with an association         constant (K_(A)) of 10⁵ to 10¹² liter/moles or more, and         preferably 10⁷ to 10¹² liter/moles or more and more preferably         10⁸ to 10¹² liter/moles);         and/or such that they:     -   bind to an extracellular part, region, domain, loop or other         extracellular epitope of one of the Targets of the invention (as         described herein) or against a peptide derived therefrom with a         k_(on)-rate of between 10² M⁻¹s⁻¹ to about 10⁷ M⁻¹s⁻¹,         preferably between 10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more preferably         between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, such as between 10⁵ M⁻¹s⁻¹         and 10⁷ M⁻¹s⁻¹;         and/or such that they:     -   bind to an extracellular part, region, domain, loop or other         extracellular epitope of one of the Targets of the invention (as         described herein) or against a peptide derived therefrom with a         k_(off) rate between 1 s⁻¹ (t_(1/2)=0.69 s) and 10⁻⁶ s⁻¹         (providing a near irreversible complex with a t_(1/2) of         multiple days), preferably between 10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more         preferably between 10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as between 10⁻⁴         s⁻¹ and 10⁻⁶ s⁻¹.

Preferably, a monovalent amino acid sequence of the invention (or a polypeptide that contains only one amino acid sequence of the invention) is preferably such that it will bind to an extracellular part, region, domain, loop or other extracellular epitope of one of the Targets of the invention (as described herein) with an affinity less than 500 nM, preferably less than 200 nM, more preferably less than 10 nM, such as less than 500 pM.

Also, according to this aspect, any multivalent or multispecific (as defined herein) polypeptides of the invention may also be suitably directed against two or more different extracellular parts, regions, domains, loops or other extracellular epitopes on the same antigen, for example against two different extracellular loops, against two different extracellular parts of the transmembrane domains or against one extracellular loops and one extracellular loop. Such multivalent or multispecific polypeptides of the invention may also have (or be engineered and/or selected for) increased avidity and/or improved selectivity for one of the desired Targets of the invention, and/or for any other desired property or combination of desired properties that may be obtained by the use of such multivalent or multispecific polypeptides.

Generally, it is expected that amino acid sequences and polypeptides of the invention that are directed against an extracellular loop or domain of one of the Targets of the invention (or against a small peptide derived therefrom or based thereon), and/or that have been screened against, selected using and/or raised against an extracellular loop or domain of one of the Targets of the invention (or against a small peptide derived therefrom or based thereon) will also be able to bind (and in particular, to specifically bind, as defined herein) to such an extracellular loop or domain (or peptide derived therefrom) that forms part of one of the Targets of the invention (or at least one subunit thereof) that is present on the surface of a cell. Thus, such (peptides derived from) an extracellular loop or domain may find particular use in methods for generating amino acid sequences and polypeptides of the invention (as defined herein); and such methods and uses form further aspects of the invention; as do amino acid sequences. Nanobodies and polypeptides of the invention that are directed against or raised against such an extracellular loop, domain or peptide derived therefrom.

For example, such a method may comprises the following:

-   a) a step of suitably immunizing a Camelid with a suitable antigen     that comprises the desired extracellular part, region, domain, loop     or other extracellular epitope(s), or with a suitable peptide     derived therefrom or based thereon, such that an immune response     against the desired extracellular part, region, domain, loop or     other extracellular epitope(s) is raised. The antigen may be any     suitable antigen that is capable of raising an immune response     against the desired extracellular part, region, domain, loop or     other extracellular epitope(s); such as, for example and without     limitation, whole cells that are alive and overexpress the desired     extracellular part, region, domain, loop or other extracellular     epitope(s) on their surface in their native confirmation, cell wall     fragments thereof or any other suitable preparation derived from     such cells, vesicles that have the desired extracellular part,     region, domain, loop or other extracellular epitope(s) on their     surface, a subunit or fragment of a subunit of one of the Targets of     the invention, that comprises the desired extracellular part,     region, domain, loop or other extracellular epitope(s), or a     synthetic or semi-synthetic peptide that comprises and/or is based     on (the amino acid sequence of) the desired extracellular part,     region, domain, loop or other extracellular epitope(s), more     preferably, whole cells (e.g. HEK293) that are alive and overexpress     the desired extracellular part, region, domain, loop or other     extracellular epitope(s) on their surface in their native     confirmation; and -   b) a step of selection for binding for the desired extracellular     part, region, domain, loop or other extracellular epitope(s) using     cell membranes preparation of different (than the one using in     immunization) and several cell types overexpressing one of the     Targets of the invention. This may for example be performed by     selecting from a set, a collection or a library of cells that     express heavy chain antibodies on their surface (e.g. B-cells     obtained from a suitably immunized Camelid) and using a cell     membranes preparation of e.g. a first type of cells such as e.g. CHO     for a first round selection and e.g. a second type of cells such as     e.g. COS-7 cells for a second round selection; by selecting from a     (naïve or immune) library of VHH sequences or Nanobody sequences by     using a cell membranes preparation of e.g. a first type of cell such     as e.g. CHO for a first round selection and e.g. a second type of     cell such as e.g. COS-7 cell for a second round selection; or by     selecting from a (naïve or immune) library of nucleic acid sequences     that encode VHH sequences or Nanobody sequences by using a cell     membranes preparation of e.g. a first type of cell such as e.g. CHO     for a first round selection and e.g. a second type of cells such as     e.g. COS-7 cell for a second round selection; which may all be     performed in a manner known per se; and optionally -   c) washing only mildly with a buffer such as PBS without detergents;     and which method may optionally further comprise one or more other     suitable steps known per se, such as, for example and without     limitation, a step of affinity maturation, a step of expressing the     desired amino acid sequence, a step of screening for binding and/or     for activity against the desired antigen (in this case, against one     of the Targets of the invention), a step of determining the desired     amino acid sequence or nucleotide sequence, a step of introducing     one or more humanizing substitutions (e.g. as further described     herein), a step of formatting in a suitable multivalent and/or     multispecific format, a step of screening for the desired biological     and/or physiological properties (i.e. using a suitable assay, such     as those described herein); and/or any suitable combination of one     or more of such steps, in any suitable order.

Such methods and the amino acid sequences obtained via such methods, as well as proteins and polypeptides comprising or essentially consisting of the same, form further aspects of this invention.

The amino acid sequences, Nanobodies and polypeptides of the invention may also bind to one of the Targets of the invention at the same site as the endogenous agonist (i.e. at an orthosteric site).

The amino acid sequences, Nanobodies and polypeptides of the invention may also bind to one of the Targets of the invention in such a way that they block adhesion and/or fusion of a virus and/or bacteria.

The amino acid sequences, Nanobodies and polypeptides of the invention may also bind to of one of the Targets of the invention in such a way that they mediate allosteric modulation (e.g. bind to one of the Targets of the invention at an allosteric site).

The amino acid sequences, Nanobodies and polypeptides of the invention may also bind to one of the Targets of the invention in such a way that they inhibit or enhance the assembly of one of the Targets of the invention functional homodimers or heterodimers and thus prevent adhesion and/or fusion of a virus and/or bacteria.

More specifically, the amino acid sequences and polypeptides according to the present invention may neutralize a virus (as defined herein) and/or modulate, reduce and/or inhibit the infectivity of a virus (as defined herein). Accordingly, the amino acid sequences and polypeptides of the present invention that neutralize a virus (as defined herein) and/or modulate, reduce and/or inhibit the infectivity of a virus (as defined herein) in the pre-entry phase of viral infection (i.e. before and/or during viral entry in a target host cell has taken place), are said herein to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

The invention also relates to the use of an one amino acid sequence, Nanobody, compound or polypeptide of the invention in the preparation of a composition (such as, without limitation, a pharmaceutical composition or preparation as further described herein) for modulating viral entry and/or for modulating the biological pathways that are mediated by the Target of the invention, either in vitro (e.g. in an in vitro or cellular assay) or in vivo (e.g. in an a single cell or multicellular organism, and in particular in a mammal, and more in particular in a human being, such as in a human being that is at risk of or suffers from a viral disease.

In the context of the present invention, “modulating” or “to modulate” generally means either reducing, preventing or inhibiting viral entry and/or reducing, preventing or inhibiting the biological pathways that are mediated by a Target of the invention and/or its ligand, as measured using a suitable in vitro, cellular or in vivo assay (such as those mentioned herein). In particular, “modulating” or “to modulate” may mean either reducing, preventing or inhibiting viral entry and/or reducing, preventing or inhibiting the biological pathways that are mediated by the Target of the invention and/or its ligand as measured using a suitable in vitro, cellular or in vivo assay (such as those mentioned herein), by at least 1%, preferably at least 5%, such as at least 10% or at least 25%, for example by at least 50%, at least 60%, at least 70%, at least 80%, or 90% or more, compared to normal (i.e. naturally occurring) viral entry and/or normal (i.e. naturally occurring) biological pathways that are mediated by the Target of the invention and/or its ligand in the same assay under the same conditions but without the presence of the amino acid sequence, Nanobody, compound or polypeptide of the invention.

As will be clear to the skilled person, “modulating” may also involve effecting a change (which may either be an increase or a decrease) in binding specificity and/or selectivity of the Target of the invention for one or more of its binding partners; and/or effecting a change (which may either be an increase or a decrease) in the sensitivity of a Target of the invention for one or more conditions in the medium or surroundings in which an Target of the invention is present (such as pH, ion strength, the presence of co-factors, etc.), compared to the same conditions but without the presence of the amino acid sequence, Nanobody, compound or polypeptide of the invention. As will be clear to the skilled person, this may again be determined in any suitable manner and/or using any suitable assay known per se, such as the assays described herein or in the prior art cited herein.

“Modulating” may also mean effecting a change with respect to one or more biological or physiological mechanisms, effects, responses, functions, pathways or activities in which the Target of the invention (or in which its binding partners or pathway(s)) are involved. Again, as will be clear to the skilled person this may be determined in any suitable manner and/or using any suitable (in vitro and usually cellular or in assay) assay known per se, such as the assays described herein or in the prior art cited herein. In particular, with respect to one or more biological or physiological mechanisms, effects, responses, functions, pathways or activities in which the Target of the invention and/or its ligand is involved, effecting a change can mean a change by at least 1%, preferably at least 5%, such as at least 10% or at least 25%, for example by at least 50%, at least 60%, at least 70%, at least 80%, or 90% or more, compared to the biological or physiological mechanisms, effects, responses, functions, pathways or activities in the same assay under the same conditions but without the presence of the amino acid sequence, Nanobody, compound or polypeptide of the invention.

Modulating may be reversible or irreversible, but for pharmaceutical and pharmacological purposes will usually be in a reversible manner.

Accordingly, the present invention also relates to amino acid sequences and polypeptides that can be used to modulate, and in particular to inhibit and/or to prevent the viral-mediated biological pathways in which a Target of the invention is involved. In particular, the amino acid sequences and polypeptides of the present invention can be used to neutralize a virus (as defined herein) and/or to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein).

More specifically, the amino acid sequences and polypeptides according to the present invention may neutralize a virus (as defined herein) and/or modulate, reduce and/or inhibit the infectivity of a virus (as defined herein) in the pre-entry phase of viral infection (i.e. before and/or during viral entry in a target host cell has taken place) and/or in the post-entry phase of viral infection (i.e. after viral entry in a target host cell has taken place). Accordingly, the amino acid sequences and polypeptides of the present invention that neutralize a virus (as defined herein) and/or modulate, reduce and/or inhibit the infectivity of a virus (as defined herein) in the pre-entry phase of viral infection (i.e. before and/or during viral entry in a target host cell has taken place), are said herein to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell. The amino acid sequences and polypeptides according to the present invention may neutralize virus by at least 1%, preferably at least 5%, such as at least 10% or at least 25%, for example by at least 50%, at least 60%, at least 70%, at least 80%, or 90% or more, compared to virus neutralization under the same conditions but without the presence of the amino acid sequence, Nanobody, compound or polypeptide of the invention. The neutralization may be increased by at least 2 times, preferably at least 3 times, such as at least 5 times or at least 10 times, for example by at least 15 times, at least 20 times, at least 30 times, at least 50 times, or 100 times or more, compared to virus neutralization under the same conditions but without the presence of the amino acid sequence, Nanobody, compound or polypeptide of the invention. The amino acid sequences and polypeptides according to the present invention may modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell by at least 1%, preferably at least 5%, such as at least 10% or at least 25%, for example by at least 50%, at least 60%, at least 70%, at least 80%, or 90% or more, compared to viral entry in a target host under the same conditions but without the presence of the amino acid sequence, Nanobody, compound or polypeptide of the invention.

In a specific aspect, the present invention relates to multivalent (such as bivalent, biparatopic, bispecific, trivalent, triparatopic, trispecific, as further defined herein) amino acid sequences and polypeptides that modulate, and in particular to inhibit and/or to prevent the viral-mediated biological pathways a Target of the invention is involved. In particular, the multivalent (preferably bivalent, more preferably trivalent) amino acid sequences and polypeptides of the present invention can neutralize a virus (as defined herein), modulate, reduce and/or inhibit the infectivity of a virus (as defined herein), and/or modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell. In one aspect, these multivalent (preferably bivalent, more preferably trivalent) amino acid sequences and polypeptides are directed against hCXCR4 and show increased in vitro and/or in vivo neutralization of HIV (as e.g. measured by HIV infection assay such as described herein) compared to the corresponding monovalent amino acid sequence. The neutralization may be increased by at least 2 times, preferably at least 3 times, such as at least 5 times or at least 10 times, for example by at least 15 times, at least 20 times, at least 30 times, at least 50 times, or 100 times or more, compared to the neutralization in the same assay under the same conditions by the corresponding monovalent amino acid sequence. In another aspect, these multivalent (preferably bivalent, more preferably trivalent) amino acid sequences and polypeptides are directed against hCD4 and show increased in vitro and/or in vivo neutralization of HIV (as e.g. measured by a HIV infection assay as described herein) compared to the corresponding monovalent amino acid sequence. The neutralization may be increased by at least 2 times, preferably at least 3 times, such as at least 5 times or at least 10 times, for example by at least 15 times, at least 20 times, at least 30 times, at least 50 times, or 100 times or more, compared to the neutralization in the same assay under the same conditions by the corresponding monovalent amino acid sequence.

In yet another aspect, these multivalent (preferably bivalent, more preferably trivalent) amino acid sequences and polypeptides are directed against hCXCR4 and show increased competition with CXCL12 for binding hCXCR4 compared to the corresponding monovalent amino acid sequence. The competition may be increased by at least 2 times, preferably at least 3 times, such as at least 5 times or at least 10 times, for example by at least 15 times, at least 20 times, at least 30 times, at least 50 times, or 100 times or more, compared to the competition in the same assay under the same conditions by the corresponding monovalent amino acid sequence.

In yet another aspect, these multivalent (preferably bivalent, more preferably trivalent) amino acid sequences and polypeptides are directed against hCD4 and show increased competition with gp120 for binding hCD4 compared to the corresponding monovalent amino acid sequence. The competition may be increased by at least 2 times, preferably at least 3 times, such as at least 5 times or at least 10 times, for example by at least 15 times, at least 20 times, at least 30 times, at least 50 times, or 100 times or more, compared to the competition in the same assay under the same conditions by the corresponding monovalent amino acid sequence.

Accordingly, the amino acid sequences and (multivalent) polypeptides of the present invention can modulate and in particular inhibit and/or prevent viral entry in a target host cell by specifically binding to a Target of the invention; preferably, the amino acid sequences and polypeptides of the present invention can modulate and in particular inhibit and/or prevent viral entry in a target host cell by binding to a Target of the invention, such that virion attachment to a target host cell is modulated, inhibited and/or prevented (for instance by modulating and/or inhibiting and/or preventing the interaction between an envelope protein of a virus and the Target of the invention on a target host cell and/or the interaction between the an envelope protein of a virus and a target host cell or by competing with an envelope protein for binding to the Target of the invention or said target host cell). In a preferred aspect, viral entry in a target host cell is modulated and in particular inhibited and/or prevented by at least 1%, preferably at least 5%, such as at least 10% or at least 25%, for example by at least 50%, at least 60%, at least 70%, at least 80%, or 90% or more, compared to prevent viral entry in a target host under the same conditions but without the presence of the amino acid sequence, Nanobody, compound or polypeptide of the invention.

A further aspect of the invention relates to a multispecific polypeptide of the invention (as defined herein) that comprises at least one amino acid sequence of the invention (such as a Nanobody) against one of the Targets of the invention. Such multispecific proteins may further be as described herein.

In a preferred embodiment, the amino acid sequence or polypeptide of the invention is a “monoclonal” amino acid sequence or polypeptide, by which is meant that at least each of the one or more amino acid sequences directed against the Target of the invention that are present in said protein or polypeptide (and preferably all of the immunoglobulin sequences that are present in said protein or polypeptide) are “monoclonal” as commonly understood by the skilled person. In this respect, it should however be noted that, as further described herein, the present invention explicitly covers multivalent or multispecific proteins that comprise two or more immunoglobulin sequences (and in particular monoclonal immunoglobulin sequences) that are directed against different parts, regions, domains, loops or epitopes of the same Target of the invention, and in particular against different extracellular parts, regions, domains, loops or epitopes of the same Target of the invention.

It is also within the scope of the invention that, where applicable, an amino acid sequence of the invention can bind to two or more antigenic determinants, epitopes, parts, domains, subunits or confirmations of Targets of the invention. In such a case, the antigenic determinants, epitopes, parts, domains or subunits of Targets of the invention to which the amino acid sequences and/or polypeptides of the invention bind may be essentially the same (for example, if Targets of the invention contain repeated structural motifs or occurs in a multimeric form) or may be different (and in the latter case, the amino acid sequences and polypeptides of the invention may bind to such different antigenic determinants, epitopes, parts, domains, subunits of Targets of the invention with an affinity and/or specificity which may be the same or different). Also, for example, when Targets of the invention exists in an activated conformation and in an inactive conformation, the amino acid sequences and polypeptides of the invention may bind to either one of these confirmation, or may bind to both these confirmations (i.e. with an affinity and/or specificity which may be the same or different). Also, for example, the amino acid sequences and polypeptides of the invention may bind to a conformation of Targets of the invention in which it is bound to a pertinent ligand, may bind to a conformation of Targets of the invention in which it not bound to a pertinent ligand, or may bind to both such conformations (again with an affinity and/or specificity which may be the same or different).

As further described herein, a polypeptide of the invention may be bivalent and/or multivalent (as defined herein) and contain two or more amino acid sequences of the invention that are directed against a Target of the invention. Generally, such polypeptides will bind to the Target of the invention with increased avidity compared to a single amino acid sequence of the invention. It has also been observed that such polypeptides show (synergistically) increased binding, competition, and/or in vitro and/or in vivo neutralization of the virus.

Such a polypeptide may for example comprise two amino acid sequences of the invention that are directed against the same antigenic determinant, epitope, part, domain, subunit or conformation (where applicable) of a Target of the invention (which may or may not be an interaction site); or such a polypeptide may be biparatopic and/or multiparatopic (as defined herein) and comprise at least one “first” amino acid sequence of the invention that is directed against a first antigenic determinant, epitope, part, domain, subunit or conformation (where applicable) of a Target of the invention (which may or may not be an interaction site); and at least one “second” amino acid sequence of the invention that is directed against a second antigenic determinant, epitope, part, domain, subunit or conformation (where applicable) of said Target of the invention, wherein said second antigenic determinant, epitope, part, domain, subunit or conformation is different from the first (and again may or may not be an interaction site). Preferably, in such “bi- and/or multiparatopic” polypeptides of the invention, at least one amino acid sequence of the invention is directed against an interaction site (as defined herein), although the invention in its broadest sense is not limited thereto.

It is thus also within the scope of the invention that, where applicable, a polypeptide of the invention can bind to two or more antigenic determinants, epitopes, parts, domains, subunits or conformations of a Target of the invention. In such a case, the antigenic determinants, epitopes, parts, domains or subunits of said Target of the invention to which the amino acid sequences and/or polypeptides of the invention bind may be essentially the same (for example, if a Target of the invention contains repeated structural motifs or occurs in a multimeric form) or may be different (and in the latter case, the amino acid sequences and polypeptides of the invention are said to be “bi- and/or multiparatopic” and may bind to such different antigenic determinants, epitopes, parts, domains, subunits of said Target of the invention with an affinity and/or specificity which may be the same or different). Accordingly, bi- or multiparatopic polypeptides of the present invention are directed against and/or specifically bind to at least two epitopes of a Target of the invention, and are for example (but not limited to) polypeptides that are directed against and/or can specifically bind to three or even more epitopes of the same Target of the invention.

For example, and generally, a bivalent polypeptide of the invention may comprise two amino acid sequences of the invention directed against an antigenic determinant, epitope, part or domain of the Target of the invention which may be suitably linked, for example via a suitable linker as further described herein. Preferably, such a bivalent polypeptide of the invention is further such that, when it binds to the Target of the invention, it is capable of simultaneously binding to both antigenic determinants, epitopes, parts or domains (i.e. via the two amino acid sequences of the invention capable of binding to said antigenic determinants, epitopes, parts or domains). Examples of such bivalent polypeptides of the invention will become clear from the further description herein. Also, a trivalent polypeptide of the invention may comprise three amino acid sequences of the invention directed against an antigenic determinant, epitope, part or domain of the viral envelope protein, and generally multivalent polypeptides of the invention may contain at least two amino acid sequences of the invention directed against an antigenic determinants, epitopes, parts or domains of the viral envelope protein. Generally, such bivalent, trivalent and multivalent polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bivalent, trivalent and multivalent polypeptides of the invention (for example, these bivalent, trivalent and multivalent polypeptides of the invention preferably comprise single variable domains and more preferably Nanobodies).

In one aspect of the invention, the amino acid sequences and (in particular) polypeptides of the invention are capable of binding to two or more antigenic determinants, epitopes, parts, domains of an envelope protein of a virus which are essentially the same. In this context, the amino acid sequences and polypeptides of the invention are also referred to as “multivalent (monospecific)” (such as e.g. “bivalent (monospecific)” or “trivalent (monospecific)”, etc.) amino acid sequences and polypeptides. The multivalent amino acid sequences and polypeptides of the invention can be directed against any antigenic determinants, epitopes, parts, and/or domains of the envelope protein of a virus.

In a preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bivalent and are directed against the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding to hCXCR4.

Generally, such a bivalent polypeptide of the invention may contain two amino acid sequences of the invention that are capable of binding to the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding to hCXCR4. Generally, such bivalent polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bivalent polypeptides of the invention (for example, these bivalent polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind the CXCL12 binding site; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bivalent and are at least capable, upon binding to hCXCR4, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bivalent and are directed against the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4.

Generally, such a bivalent polypeptide of the invention will contain two amino acid sequences of the invention that are capable of binding to the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4. Generally, such bivalent polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bivalent polypeptides of the invention (for example, these bivalent polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind the gp120 binding site; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bivalent and are at least capable, upon binding to hCD4, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In a preferred aspect, the amino acid sequences and (in particular) polypeptides of the invention are capable of binding to two or more different antigenic determinants, epitopes, parts, domains of a Target of the invention. In this context, the amino acid sequences and polypeptides of the invention are also referred to as “multiparatopic” (such as e.g. “biparatopic” or “triparatopic”, etc.) amino acid sequences and polypeptides. The multiparatopic amino acid sequences and polypeptides of the invention can be directed against any antigenic determinants, epitopes, parts, and/or domains of the Target of the invention.

For example, and generally, a biparatopic polypeptide of the invention may comprise at least one amino acid sequence of the invention directed against a first antigenic determinant, epitope, part or domain of the Target of the invention and at least one amino acid sequence of the invention directed against a second antigenic determinant, epitope, part or domain of the Target of the invention different from the first antigenic determinant, epitope, part or domain (in which said amino acid sequences may be suitably linked, for example via a suitable linker as further described herein). Preferably, such a biparatopic polypeptide of the invention is further such that, when it binds to the Target of the invention, it is capable of simultaneously binding to the first antigenic determinant, epitope, part or domain (i.e. via the at least one amino acid sequence of the invention capable of binding to said first antigenic determinant, epitope, part or domain) and binding to said second antigenic determinant, epitope, part or domain (i.e. via the at least one amino acid sequence of the invention capable of binding to said second antigenic determinant, epitope, part or domain). Examples of such biparatopic polypeptides of the invention will become clear from the further description herein. Also, a triparatopic polypeptide of the invention may comprise at least one further amino acid sequence of the invention directed against a third antigenic determinant, epitope, part or domain of the Target of the invention (different from both the first and second antigenic determinant, epitope, part or domain), and generally multiparatopic polypeptides of the invention may contain at least two amino acid sequences of the invention directed against at least two different antigenic determinants, epitopes, parts or domains of the Target of the invention. Generally, such biparatopic, triparatopic and multiparatopic polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these biparatopic, triparatopic and multiparatopic polypeptides of the invention (for example, these biparatopic, triparatopic and multiparatopic polypeptides of the invention preferably comprise single variable domains and more preferably Nanobodies).

In a preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are biparatopic (or multiparatopic) and are directed against the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding to hCXCR4, as well as against at least one other antigenic determinant, epitope, part or domain on hCXCR4.

Generally, such a biparatopic (or multiparatopic) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding to hCXCR4, as well as at least one further amino acid sequence of the invention that is capable of binding to at least one other antigenic determinant, epitope, part or domain on hCXCR4. Generally, such biparatopic (or multiparatopic) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these biparatopic (or multiparatopic) polypeptides of the invention (for example, these biparatopic and multiparatopic polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind the CXCL12 binding site and the at least one other antigenic determinant, epitope, part or domain on hCXCR4; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are biparatopic (or multiparatopic) and are at least capable, upon binding to hCXCR4, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and polypeptides of the invention are biparatopic (or multiparatopic) and are directed against the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4, as well as against at least one other antigenic determinant on hCD4.

Generally, such a biparatopic (or multiparatopic) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4, as well as at least one further amino acid sequence of the invention that is capable of binding to at least one other antigenic determinant, epitope, part or domain on hCD4. Generally, such biparatopic (or multiparatopic) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these biparatopic (or multiparatopic) polypeptides of the invention (for example, these biparatopic and multiparatopic polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind the gp120 binding site and the at least one other antigenic determinant, epitope, part or domain on hCD4; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are biparatopic (or multiparatopic) and are at least capable, upon binding to hCD4, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are biparatopic with both paratopes directed against the CXCL12 binding site on hCXCR4.

Generally, such a biparatopic (or multiparatopic) polypeptide of the invention will contain two amino acid sequences of the invention that are capable of binding to the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding to hCXCR4. Generally, such biparatopic (or multiparatopic) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these biparatopic (or multiparatopic) polypeptides of the invention (for example, these biparatopic and multiparatopic polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind the CXCL12 binding site on hCXCR4; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are biparatopic with both paratopes directed against the gp120 binding site on hCD4.

Generally, such a biparatopic (or multiparatopic) polypeptide of the invention will contain two amino acid sequences of the invention that are capable of binding to the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4. Generally, such biparatopic (or multiparatopic) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these biparatopic (or multiparatopic) polypeptides of the invention (for example, these biparatopic and multiparatopic polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind the gp120 binding site on hCD4; and preferably comprise single variable domains and more preferably Nanobodies).

Also, the polypeptides of the present invention may also be directed against and/or can specifically bind to at least one particular Target of the invention and at least one further epitope of another Target of the invention, which is different from said at least one particular Target of the invention. Thus, the polypeptides according to the invention may be directed against and/or may specifically bind to at least two (or even more) epitopes of at least two different Targets of the invention. Also, said at least one further epitope may or may not be involved in viral entry in a target host cell.

Generally, bi-, and multivalent (as defined herein), bi-, and multispecific (as defined herein) and bi-, and multiparatopic (as defined herein) polypeptides according to the invention may be useful for the prevention and/or treatment of viral diseases by specifically binding to at least one epitope of a Target of the invention and at least one further epitope (which may or may not be different from said at least one epitope) of the Target of the invention.

Preferably, bi-, and multiparatopic polypeptides (as defined herein) according to the invention may be useful for the prevention and/or treatment of viral diseases by specifically binding to at least two (or even more) epitopes (which may be the same or different) on the same Target of the invention.

Alternatively, the polypeptides of the present invention may be directed against and/or can specifically bind to at least one epitope of a Target of the invention and at least one further epitope of another target, which is different from said Target of the invention and which is for instance a further Target of the invention.

In a preferred, but non-limiting aspect, the amino acid sequences and polypeptides of the invention are bispecific (or multispecific) and are directed against an antigenic determinant, epitope, part or domain on hCXCR4 as well as against an antigenic determinant, epitope, part or domain on on hCD4. Generally, such a bispecific (or multispecific) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCXCR4, as well at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCD4. Generally, such bispecific (or multispecific) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bispecific (or multispecific) polypeptides of the invention (for example, these bispecific and multispecific polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind both binding sites; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bispecific (or multispecific) and are at least capable, upon binding, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and polypeptides of the invention are bispecific (or multispecific) and are directed against the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding hCXCR4 as well as against an antigenic determinant, epitope, part or domain on hCD4.

Generally, such a bispecific (or multispecific) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding hCXCR4, as well at least one amino acid sequence of the invention that is capable of binding to an antigenic determinant, epitope, part or domain on on hCD4. Generally, such bispecific (or multispecific) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bispecific (or multispecific) polypeptides of the invention (for example, these bispecific and multispecific polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind both binding sites; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bispecific (or multispecific) and are at least capable, upon binding, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and polypeptides of the invention are bispecific (or multispecific) and are directed against an antigenic determinant, epitope, part or domain on on hCXCR4, as well as against the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4.

Generally, such a bispecific (or multispecific) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to an antigenic determinant, epitope, part or domain on on hCXCR4, as well at least one amino acid sequence of the invention that is capable of binding to the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4. Generally, such bispecific (or multispecific) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bispecific (or multispecific) polypeptides of the invention (for example, these bispecific and multispecific polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind both binding sites; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bispecific (or multispecific) and are at least capable, upon binding, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and polypeptides of the invention are bispecific (or multispecific) and are directed against the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding hCXCR4 as well as against the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4.

Generally, such a bispecific (or multispecific) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to the CXCL12 binding site on hCXCR4 and/or capable of competing with CXCL12 for binding hCXCR4, as well at least one amino acid sequence of the invention that is capable of binding to the gp120 binding site on hCD4 and/or capable of competing with gp120 for binding to hCD4. Generally, such bispecific (or multispecific) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bispecific (or multispecific) polypeptides of the invention (for example, these bispecific and multispecific polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind both binding sites; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bispecific (or multispecific) and are at least capable, upon binding, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and polypeptides of the invention are bispecific (or multispecific) and are directed against an antigenic determinant, epitope, part or domain on hCXCR4 as well as against an antigenic determinant, epitope, part or domain on on hCCR5. Generally, such a bispecific (or multispecific) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCXCR4, as well at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCCR5. Generally, such bispecific (or multispecific) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bispecific (or multispecific) polypeptides of the invention (for example, these bispecific and multispecific polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind both binding sites; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bispecific (or multispecific) and are at least capable, upon binding, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and polypeptides of the invention are bispecific (or multispecific) and are directed against an antigenic determinant, epitope, part or domain on hCD4 as well as against an antigenic determinant, epitope, part or domain on on hCCR5. Generally, such a bispecific (or multispecific) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCD4, as well at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCCR5. Generally, such bispecific (or multispecific) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these bispecific (or multispecific) polypeptides of the invention (for example, these bispecific and multispecific polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind both binding sites; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are bispecific (or multispecific) and are at least capable, upon binding, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

In another preferred, but non-limiting aspect, the amino acid sequences and polypeptides of the invention are trispecific (or multispecific) and are directed against an antigenic determinant, epitope, part or domain on hCXCR4, against an antigenic determinant, epitope, part or domain on on hCD4, as well as against an antigenic determinant, epitope, part or domain on on hCCR5. Generally, such a tripecific (or multispecific) polypeptide of the invention will contain at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCXCR4, at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCD4, as well at least one amino acid sequence of the invention that is capable of binding to the antigenic determinant, epitope, part or domain on hCCR5. Generally, such tripecific (or multispecific) polypeptides of the invention may be as further described herein, and the various preferred aspects of the invention as described herein also apply to these tripecific (or multispecific) polypeptides of the invention (for example, these trispecific and multispecific polypeptides of the invention may comprise suitable linkers; are preferably such that they can simultaneously bind both binding sites; and preferably comprise single variable domains and more preferably Nanobodies).

In another preferred, but non-limiting aspect, the amino acid sequences and (in particular) polypeptides of the invention are trispecific (or multispecific) and are at least capable, upon binding, to neutralize a virus (as defined herein); to modulate, reduce and/or inhibit the infectivity of a virus (as defined herein); and/or to modulate and in particular inhibit and/or prevent viral entry (as further defined herein) in a target host cell.

It is also expected that the amino acid sequences and polypeptides of the invention will generally bind to all naturally occurring or synthetic analogs, variants, mutants, alleles, parts and fragments of Targets of the invention; or at least to those analogs, variants, mutants, alleles, parts and fragments of Targets of the invention that contain one or more antigenic determinants or epitopes that are essentially the same as the antigenic determinant(s) or epitope(s) to which the amino acid sequences and polypeptides of the invention bind in Targets of the invention (e.g. in wild-type Targets of the invention). Again, in such a case, the amino acid sequences and polypeptides of the invention may bind to such analogs, variants, mutants, alleles, parts and fragments with an affinity and/or specificity that are the same as, or that are different from (i.e. higher than or lower than), the affinity and specificity with which the amino acid sequences of the invention bind to (wild-type) Targets of the invention. It is also included within the scope of the invention that the amino acid sequences and polypeptides of the invention hind to some analogs, variants, mutants, alleles, parts and fragments of Targets of the invention, but not to others.

When Targets of the invention exists in a monomeric form and in one or more multimeric forms, it is within the scope of the invention that the amino acid sequences and polypeptides of the invention only bind to Targets of the invention in monomeric form, only bind to Targets of the invention in multimeric form, or bind to both the monomeric and the multimeric form. Again, in such a case, the amino acid sequences and polypeptides of the invention may bind to the monomeric form with an affinity and/or specificity that are the same as, or that are different from (i.e. higher than or lower than), the affinity and specificity with which the amino acid sequences of the invention bind to the multimeric form.

Also, when Targets of the invention can associate with other proteins or polypeptides to form protein complexes (e.g. with multiple subunits), it is within the scope of the invention that the amino acid sequences and polypeptides of the invention bind to Targets of the invention in its non-associated state, bind to Targets of the invention in its associated state, or bind to both. In all these cases, the amino acid sequences and polypeptides of the invention may bind to such multimers or associated protein complexes with an affinity and/or specificity that may be the same as or different from (i.e. higher than or lower than) the affinity and/or specificity with which the amino acid sequences and polypeptides of the invention bind to Targets of the invention in its monomeric and non-associated state.

Also, as will be clear to the skilled person, proteins or polypeptides that contain two or more amino acid sequences directed against Targets of the invention may bind with higher avidity to Targets of the invention than the corresponding monomeric amino acid sequence(s). For example, and without limitation, proteins or polypeptides that contain two or more amino acid sequences directed against different epitopes of Targets of the invention may (and usually will) bind with higher avidity than each of the different monomers, and proteins or polypeptides that contain two or more amino acid sequences directed against Targets of the invention may (and usually will) bind also with higher avidity to a multimer of Targets of the invention.

Generally, amino acid sequences and polypeptides of the invention will at least bind to those forms of Targets of the invention (including monomeric, multimeric and associated forms) that are the most relevant from a biological and/or therapeutic point of view, as will be clear to the skilled person.

It is also within the scope of the invention to use parts, fragments, analogs, mutants, variants, alleles and/or derivatives of the amino acid sequences and polypeptides of the invention, and/or to use proteins or polypeptides comprising or essentially consisting of one or more of such parts, fragments, analogs, mutants, variants, alleles and/or derivatives, as long as these are suitable for the uses envisaged herein. Such parts, fragments, analogs, mutants, variants, alleles and/or derivatives will usually contain (at least part of) a functional antigen-binding site for binding against Targets of the invention; and more preferably will be capable of specific binding to Targets of the invention, and even more preferably capable of binding to Targets of the invention with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein. Some non-limiting examples of such parts, fragments, analogs, mutants, variants, alleles, derivatives, proteins and/or polypeptides will become clear from the further description herein. Additional fragments or polypeptides of the invention may also be provided by suitably combining (i.e. by linking or genetic fusion) one or more (smaller) parts or fragments as described herein.

In one specific, but non-limiting aspect of the invention, which will be further described herein, such analogs, mutants, variants, alleles, derivatives have an increased half-life in serum (as further described herein) compared to the amino acid sequence from which they have been derived. For example, an amino acid sequence of the invention may be linked (chemically or otherwise) to one or more groups or moieties that extend the half-life (such as PEG), so as to provide a derivative of an amino acid sequence of the invention with increased half-life.

In one specific, but non-limiting aspect, the amino acid sequence of the invention may be an amino acid sequence that comprises an immunoglobulin fold or may be an amino acid sequence that, under suitable conditions (such as physiological conditions) is capable of forming an immunoglobulin fold (i.e. by folding). Reference is inter alia made to the review by Halaby et al., J. (1999) Protein Eng. 12, 563-71. Preferably, when properly folded so as to form an immunoglobulin fold, such an amino acid sequence is capable of specific binding (as defined herein) to Targets of the invention; and more preferably capable of binding to Targets of the invention with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein. Also, parts, fragments, analogs, mutants, variants, alleles and/or derivatives of such amino acid sequences are preferably such that they comprise an immunoglobulin fold or are capable for forming, under suitable conditions, an immunoglobulin fold.

In particular, but without limitation, the amino acid sequences of the invention may be amino acid sequences that essentially consist of 4 framework regions (FR1 to FR4 respectively) and 3 complementarity determining regions (CDR1 to CDR3 respectively); or any suitable fragment of such an amino acid sequence (which will then usually contain at least some of the amino acid residues that form at least one of the CDR's, as further described herein).

The amino acid sequences of the invention may in particular be an immunoglobulin sequence or a suitable fragment thereof, and more in particular be an immunoglobulin variable domain sequence or a suitable fragment thereof, such as light chain variable domain sequence (e.g. a V_(L)-sequence) or a suitable fragment thereof; or a heavy chain variable domain sequence (e.g. a V_(H)-sequence) or a suitable fragment thereof. When the amino acid sequence of the invention is a heavy chain variable domain sequence, it may be a heavy chain variable domain sequence that is derived from a conventional four-chain antibody (such as, without limitation, a V_(H) sequence that is derived from a human antibody) or be a so-called V_(HH)-sequence (as defined herein) that is derived from a so-called “heavy chain antibody” (as defined herein).

However, it should be noted that the invention is not limited as to the origin of the amino acid sequence of the invention (or of the nucleotide sequence of the invention used to express it), nor as to the way that the amino acid sequence or nucleotide sequence of the invention is (or has been) generated or obtained. Thus, the amino acid sequences of the invention may be naturally occurring amino acid sequences (from any suitable species) or synthetic or semi-synthetic amino acid sequences. In a specific but non-limiting aspect of the invention, the amino acid sequence is a naturally occurring immunoglobulin sequence (from any suitable species) or a synthetic or semi-synthetic immunoglobulin sequence, including but not limited to “humanized” (as defined herein) immunoglobulin sequences (such as partially or fully humanized mouse or rabbit immunoglobulin sequences, and in particular partially or fully humanized. V_(HH) sequences or Nanobodies), “camelized” (as defined herein) immunoglobulin sequences, as well as immunoglobulin sequences that have been obtained by techniques such as affinity maturation (for example, starting from synthetic, random or naturally occurring immunoglobulin sequences), CDR grafting, veneering, combining fragments derived from different immunoglobulin sequences, PCR assembly using overlapping primers, and similar techniques for engineering immunoglobulin sequences well known to the skilled person; or any suitable combination of any of the foregoing. Reference is for example made to the standard handbooks, as well as to the further description and prior art mentioned herein.

Similarly, the nucleotide sequences of the invention may be naturally occurring nucleotide sequences or synthetic or semi-synthetic sequences, and may for example be sequences that are isolated by PCR from a suitable naturally occurring template (e.g. DNA or RNA isolated from a cell), nucleotide sequences that have been isolated from a library (and in particular, an expression library), nucleotide sequences that have been prepared by introducing mutations into a naturally occurring nucleotide sequence (using any suitable technique known per se, such as mismatch PCR), nucleotide sequence that have been prepared by PCR using overlapping primers, or nucleotide sequences that have been prepared using techniques for DNA synthesis known per se.

The amino acid sequence of the invention may in particular be a domain antibody (or an amino acid sequence that is suitable for use as a domain antibody), a single domain antibody (or an amino acid sequence that is suitable for use as a single domain antibody), a “dAb” (or an amino acid sequence that is suitable for use as a dAb) or a Nanobody (as defined herein, and including but not limited to a V_(HH) sequence); other single variable domains, or any suitable fragment of any one thereof. For a general description of (single) domain antibodies, reference is also made to the prior art cited above, as well as to EP 0 368 684. For the term “dAb's”, reference is for example made to Ward et al. (Nature 1989 Oct. 12; 341 (6242): 544-6), to Holt et al., Trends Biotechnol., 2003, 21(10:484-490; as well as to for example WO 06/030220, WO 06/003388 and other published patent applications of Domantis Ltd. It should also be noted that, although less preferred in the context of the present invention because they are not of mammalian origin, single domain antibodies or single variable domains can be derived from certain species of shark (for example, the so-called “IgNAR domains”, see for example WO 05/18629).

In particular, the amino acid sequence of the invention may be a Nanobody (as defined herein) or a suitable fragment thereof. [Note: Nanobody®, Nanobodies® and Nanoclone® are registered trademarks of Ablynx N.V.] Such Nanobodies directed against Targets of the invention will also be referred to herein as “Nanobodies of the invention”.

For a general description of Nanobodies, reference is made to the further description below, as well as to the prior art cited herein. In this respect, it should however be noted that this description and the prior art mainly described Nanobodies of the so-called “V_(H)3 class” (i.e. Nanobodies with a high degree of sequence homology to human germline sequences of the V_(H)3 class such as DP-47, DP-51 or DP-29), which Nanobodies form a preferred aspect of this invention. It should however be noted that the invention in its broadest sense generally covers any type of Nanobody directed against Targets of the invention, and for example also covers the Nanobodies belonging to the so-called “V_(H)4 class” (i.e. Nanobodies with a high degree of sequence homology to human germline sequences of the V_(H)4 class such as DP-78), as for example described in WO 07/118,670.

Generally, Nanobodies (in particular V_(HH) sequences and partially humanized Nanobodies) can in particular be characterized by the presence of one or more “Hallmark residues” (as described herein) in one or more of the framework sequences (again as further described herein).

Thus, generally, a Nanobody can be defined as an amino acid sequence with the (general) structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which one or more of the Hallmark residues are as further defined herein.

In particular, a Nanobody can be an amino acid sequence with the (general) structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which the framework sequences are as further defined herein.

More in particular, a Nanobody can be an amino acid sequence with the (general) structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which:

-   i) preferably one or more of the amino acid residues at positions     1.1, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to the Kabat     numbering are chosen from the Hallmark residues mentioned in Table     A-3 below;     and in which: -   ii) said amino acid sequence has at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 1 to     22, in which for the purposes of determining the degree of amino     acid identity, the amino acid residues that form the CDR sequences     (indicated with X in the sequences of SEQ ID NO's: 1 to 22) are     disregarded.

In these Nanobodies, the CDR sequences are generally as further defined herein.

Thus, the invention also relates to such. Nanobodies that can bind to (as defined herein) and/or are directed against Targets of the invention, to suitable fragments thereof, as well as to polypeptides that comprise or essentially consist of one or more of such Nanobodies and/or suitable fragments.

SEQ ID NO's 238 to 253 give the amino acid sequences of a number of V_(HH) sequences that have been raised against human CXCR4 (Table 1).

In particular, the invention in some specific aspects provides:

-   -   amino acid sequences that are directed against (as defined         herein) a hCXCR4 and that have at least 80%, preferably at least         85%, such as 90% or 95% or more sequence identity with at least         one of the amino acid sequences of SEQ ID NO's: 238 to 253, more         preferably 238 to 239. These amino acid sequences may further be         such that they neutralize binding of the cognate ligand to         hCXCR4; and/or compete with the cognate ligand for binding to         hCXCR4; and/or are directed against an interaction site (as         defined herein) on hCXCR4 (such as the ligand binding site);     -   amino acid sequences that cross-block (as defined herein) the         binding of at least one of the amino acid sequences of SEQ ID         NO's: 238 to 253, more preferably 238 to 239 to hCXCR4 and/or         that compete with at least one of the amino acid sequences of         SEQ ID NO's: 238 to 253, more preferably 238 to 239 for binding         to hCXCR4. Again, these amino acid sequences may further be such         that they neutralize binding of the cognate ligand to hCXCR4;         and/or compete with the cognate ligand for binding to hCXCR4;         and/or are directed against an interaction site (as defined         herein) on hCXCR4 (such as the ligand binding site);

which amino acid sequences may be as further described herein (and may for example be Nanobodies); as well as polypeptides of the invention that comprise one or more of such amino acid sequences (which may be as further described herein, and may for example be bispecific and/or biparatopic polypeptides as described herein), and nucleic acid sequences that encode such amino acid sequences and polypeptides. Such amino acid sequences and polypeptides do not include any naturally occurring ligands.

SEQ ID NO's 308 to 311 give the amino acid sequences of a number of V_(HH) sequences that have been raised against human CD4 (Table 3).

In particular, the invention in some specific aspects provides:

-   -   amino acid sequences that are directed against (as defined         herein) a hCD4 and that have at least 80%, preferably at least         85%, such as 90% or 95% or more sequence identity with at least         one of the amino acid sequences of SEQ ID NO's: 308 to 311, more         preferably 311. These amino acid sequences may further be such         that they neutralize binding of the cognate ligand to hCD4;         and/or compete with the cognate ligand for binding to hCD4;         and/or are directed against an interaction site (as defined         herein) on hCD4 (such as the ligand binding site);     -   amino acid sequences that cross-block (as defined herein) the         binding of at least one of the amino acid sequences of SEQ ID         NO's: 308 to 311, more preferably 311 to hCD4 and/or that         compete with at least one of the amino acid sequences of SEQ ID         NO's: 308 to 311, more preferably 311 for binding to hCD4.         Again, these amino acid sequences may further be such that they         neutralize binding of the cognate ligand to hCD4; and/or compete         with the cognate ligand for binding to hCD4; and/or are directed         against an interaction site (as defined herein) on hCD4 (such as         the ligand binding site);

which amino acid sequences may be as further described herein (and may for example be Nanobodies); as well as polypeptides of the invention that comprise one or more of such amino acid sequences (which may be as further described herein, and may for example be bispecific and/or biparatopic polypeptides as described herein), and nucleic acid sequences that encode such amino acid sequences and polypeptides. Such amino acid sequences and polypeptides do not include any naturally occurring ligands.

TABLE 1 Nanobodies directed against human CXCR4 (SEQ ID NO: 254) SEQ ID NO: X, where X = Name Amino acid sequence 238 238C1 EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGLEWVSGIKSSGD 238D2 STRYAGSVKGRFTISRDNAKNMLYLQMYSLKPEDTAVYYCAKSRVSRTGLYTYDNR GQGTQVTVSS 239 238D4 EVQLMESGGGLVQAGGSLRLSCAASGRTFNNYAMGWFRRAPGKEREFVAAITRSGV 238G3 RSGVSAIYGDSVKDRFTISRDNAKNTLYLQMNSLKPEDTAVYTCAASAIGSGALRR FEYDYSGQGTQVTVSS 240 237B5 KVQLVESGGGLVQPGGSLRLSCAASGFAFSIHTMSWVRQAPGKGPEWVSTIKPSGD TTNYANAVKGRFTISRDNAKNTLYLQMNSLKPEDTAVYYCAKDYFGTGVRGQGTQV TVSS 241 237B6 EVQLVESGGGLVQPGGSLRLSCAASGFTFDDYAMSWVRQAPGKGLEWVSAISWNGG 237A5 STDYADSVKGRFTISRDNAKNTLYLQMNSLKSEDTAEYYCARDQGPFYSGTYYYTR 237D2 QYGYRGQGTQVTVSS 237D3 237E4 237F4 237G2 237G4 237xH5 237F1 237C5 237G1 242 238B10 EVQLVESGGGFVQAGGSLRLSCETSGRPLLGYTIAWFRQVPGKEREFVAYHRWSDG ANLYADSVKGRFTISGHNAKNTVSLQMNSLKPEDTAVYYCAAARMTTSNDKEYLYW GQGTQVTVSS 243 238C5 EVQLMESGGGLVQAGGSLRLACAASGFTFEDYAIGWFRKAPGKEREGVSCISGSDG 237G2 STTYADSVKGRFTISTDNAKNTVYLEMNSLKPEDTAVYYCAQQYGVGGRVVCPGPY 237xH5 EYDVWGQSTQVTVSS 238C3 237D6 237E6 244 238F7 EVQLVESGGGFVQAGGSLRLSCETSGRPLLGYTIAWFRQVPGKEREFVAYHRWSDG ANLYADSVKGRFTISGHNAKNTVSLQMNSLKPEDTAVYYCAAAWMTTSNDKETLYW GQGTQVTVSS 245 238H2 EVQLVESGGGLVQAGGSLRLSCAASGLTFSPSAMAWYRQGPGKERDFVASTIWSRG DTYFADSVKGRFTISRDTANYTLYLQMNNEKPEDTAVYYCSLRVRPYGQYDYWGQG TQVTVSS 246 237D4 EVQLVESGGGLVQPGGSLRLSCAASGFTFDDYAMSWVRQAPGKGLEWVSAISWNGG SADYADSVKGRFTISRDNAKNTLYLQMNSLKSEDTAVYYCAKDQGPFYSGTYYYTK GYAYWGQGTQVTVSS 247 238F3 EVQLVESGGGLAQAGGSLRLSCAASGRTYAMGWFRQAPGKEREFVTTSRLITDNII YADSVKGRFTLTRDNGKNTVYLQMDSLKPDDTAVYFCAARQNYSRSVFGAKDYDYW GQGTQVTVSS 248 237A6 EVQLVESGGGLVQAGGSLRLSCAASGSIFSLNAMGWYRQAPGKQRELVAGITSSTS TYYADSVKGRFTISRDNTKNTVYLQMNSLKPEDTAVYYCNVDCPDYYSDYECPLED RGQGTQVTVSS 249 237D1 EVQLVESGGGLAQPGGPLRLTCEASGVIYSVNDMGWYRQAPGKQRELVAVITSGGG TNYVDSVKGRFTISGDNRKKTVYLQMNSLKPEDTAVYYCSIYYSSGISTLRSWGQG TQVTVSS 250 237E1 EVQLVESGGGLVQPGGSLRLSCEVSGFTRDYYTIGWFRQAPGKEREGVSCISSSDG STAYLGSVQGRFTVSRDNAKNTVYLQMNNLKPEDTAVYYCALBSADSRCSIGSIGF TWLYNNWGQGTQVTVSS 251 23707 EVQLVESGGGLVQPGGSLRLSCAASSFIGNYHAIVWLRQAPGKELEGVSCITSRDS ITYYASFVKGRFTISRDDAKNTVYLQMNNLKPEDTAVYYCAVBTSMTCPTLIVRFN YRGQGTQVTVSS 252 23804 EVQLVESGGGLVQAGGSLRLSCKASGGTFNNYAMGWFRRAPGKEREFVAAITRSGV RSGVSAIYGDSVKDRFTISRDNVKNTLYLQMNTLKPEDTAVYTCAASAIGSGALRR FEYDYSGQGTQVTVSS 253 23701 EVQLVESGGGLVQAGGSLRLSCAASGSFFSINAMGWYRQAP0KQRELVASITSGGS TVYADSVKGRFTISRDNYNTVYLQMNSLKPEDTAVYYCNADGVPEWGKVQYPDTYR GQGTQVTVSS CDR sequences of Nanobodies directed against human CXCR4 (SEQ ID NO: 254) SEQ ID NO: CDR X, X, where X = Name where X = Amino acid sequence 142 238C1, 238D2 1 SYAMS 143 238D4, 238G3 1 NYAMG 144 237B5 1 IHTMS 145 237B6, 237A5, 237D2, 237D3, 1 DYADS 237E4, 237F4, 237G2, 237G4, 237xH5, 237F1, 237C5, 2387G1 146 238B10 1 GYTIA 147 238C5, 238G2, 238xH5, 1 DYAIG 238C3, 238D6, 238E6 148 238F7 1 GYTIA 149 238H2 1 PSAMA 150 237D4 1 DYADS 151 238F3 1 MG 152 237A6 1 LNAMG 153 237D1 1 VNDMG 154 237E1 1 YYTIG 155 237G7 1 YHAIV 156 238C4 1 NYAMG 157 237C1 1 INAMG 174 238C1, 238D2 2 GIKSSGDSTRYAGSVKG 175 238D4, 238G3 2 AITRSGVRSGVSAIYGDSVKD 176 237B5 2 TIKPSGDTTNYANAVKG 177 237B6, 237A5, 237D2, 237D3, 2 AISWNGGSTDYADSVKG 237E4, 237F4, 237G2, 237G4, 237xH5, 237F1, 237C5, 237G1 178 238B10 2 YHRWSDGANLYADSVNG 179 238C5, 238G2, 238xH5, 2 CISGSDGSTTYADSVKG 238C3, 238D6, 238E6 180 238F7 2 YHRWSDGANLYADSVKG 181 238H2 2 STIWSRGDTYFADSVKG 182 237D4 2 AISWNGGSADYADSVKG 183 238F3 2 TSRLTIDNIIYADSVKG 184 237A6 2 GITSSTSTYYADSVKG 185 237D1 2 VITSGGGTKYVDSVKG 186 237E1 2 CISSSDGSTAYLGSVQG 187 237G7 2 CITSRDSITYYASEVKG 188 238C4 2 AITRSGVRSGVSAIYGDSVKD 189 237C1 2 SITSGGSTVYADSVHG 206 238D1, 238D2 3 SRVSRTGLYTYDN 207 238D4, 238G3 3 SAIGSGALRRFEYDY 208 237B5 3 DYFGTGV 209 237B6, 237A5, 237D2, 237D3, 3 DQGPFYSGTYYYTRWGY 237E4, 237F4, 237G2, 237G4, 237xH5, 237F1, 237C5, 237G1 210 238B10 3 ARMTTSNDKEYLY 211 238C5,238G2, 238xH5, 238C3, 3 QYGVGGRVVCPGPYEYDV 238D6, 238E6 212 238F7 3 AWMTTSNDKEYLY 213 238H2 3 RVRPYGQYDY 214 237D4 3 DQGPFYSCTYYYTKGYAY 215 238F3 3 RQNYSRSVFGAKDYDY 216 237A6 3 DCPDYYSDYECPLED 217 237D1 3 YYSSGISTLRS 218 237E1 3 BSADSRCSIGSIGFTWLYNN 219 237G7 3 BTSMTCPTLIVRFNY 220 238C4 3 SAIGSGALRRFEYDY 221 237C1 3 DGVPEWSKVQYPDTY

TABLE 3 Nanobodies directed against human CD4 (SEQ ID NO: 268) SEQ ID NO: X, where X = Name Amino acid sequence 308 01B6 EVQLVESGGGLVQ5GGSLRLSCAASGFTFSGYWMYWVRQAPGKGLE WVSAISPGGGSTYYPDSVKGRFTISRDNAKNTLYLQMNSLEPEDTA LYYCASSLTATHTYEYDYWGQGTQVTVSS 309 01E2 EVQLVESGGGLVQAGGSLRLSCAASGRTSASYSMGWFRQAPGKERE FVAAISWSGDETSYADSVKGRFTIARGNAKNTVYLQMNSLKSEDTA IYYCAGDRWWRPAGLQWDYWGQGTQVTVSS 310 01H12 EVQLVESGGGLVQAGGSLKLSCAASRSILDFNAMGWYRQAPGKQRE WVTTIARAGATKYADSVKGRFSISRDNAKNTVYLQMSSLKPEDTAT YYCNARVFDLPNDYWGQGTQVTVSS 311 03F11 EVQLVESGGGSVQPGGSLTLSCGTSGRTFNVMGWFRQAPGKEREFV AAVRWSSTGIYYTQYADSVKSRFTISRDNAKNTVYLEMNSLKPEDT AVYYCAADTYNSNPARWDGYDFRGQGTQVTVSS CDR sequences of Nanobodies directed against human CD4 (SEQ ID NO: 268) SEQ ID NO: CDR X, X, where X = Name where X = Amino acid sequence 284 01B6 1 GYWMY 285 01E2 1 SYSMG 286 01H12 1 FNAMG 287 03F11 1 VMG 292 01B6 2 AISPGGGSTYYPDSVKG 293 01E2 2 AISWSGDETSYADSVKG 294 01H12 2 TIARAGATKYADSVKG 295 03F11 2 AVRWSSTGIYYTQYADSVKS 300 01B6 3 SLTATHTYEYDY 301 01E2 3 DRWWRPAGLQWDY 302 01H12 3 RVFDLPNDY 303 03F11 3 DTYNSNPARWDGYDF

Accordingly, some particularly preferred Nanobodies of the invention are Nanobodies which can bind (as further defined herein) to and/or are directed against human. CXCR4 and which:

-   i) have at least 80% amino acid identity with at least one of the     amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ     ID NO: 238 and SEQ ID NO: 239, in which for the purposes of     determining the degree of amino acid identity, the amino acid     residues that form the CDR sequences are disregarded. In this     respect, reference is also made to Table A-1, which lists the     framework 1 sequences (SEQ ID NO's: 126 to 141), framework 2     sequences (SEQ ID NO's: 158 to 173), framework 3 sequences (SEQ ID     NO's: 190 to 205) and framework 4 sequences (SEQ ID NO's: 222     to 237) of the Nanobodies of SEQ ID NO's: 238 to 253, more     preferably SEQ ID NO: 238 and SEQ ID NO: 239 (with respect to the     amino acid residues at positions 1 to 4 and 27 to 30 of the     framework 1 sequences, reference is also made to the comments made     below. Thus, for determining the degree of amino acid identity,     these residues are preferably disregarded);     and in which: -   ii) preferably one or more of the amino acid residues at positions     11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to the Kabat     numbering are chosen from the Hallmark residues mentioned in Table     A-3 below.

Accordingly, some particularly preferred Nanobodies of the invention are Nanobodies which can bind (as further defined herein) to and/or are directed against human CD4 and which:

-   iii) have at least 80% amino acid identity with at least one of the     amino acid sequences of SEQ ID NO's: 308 to 311, more preferably SEQ     ID NO: 311, in which for the purposes of determining the degree of     amino acid identity, the amino acid residues that form the CDR     sequences are disregarded. In this respect, reference is also made     to Table A-1, which lists the framework 1 sequences (SEQ ID NO's:     280 to 283), framework 2 sequences (SEQ ID NO's: 288 to 291),     framework 3 sequences (SEQ ID NO's: 296 to 299) and framework 4     sequences (SEQ ID NO's: 304 to 307) of the Nanobodies of SEQ ID     NO's: 308 to 311, more preferably SEQ ID NO: 311 (with respect to     the amino acid residues at positions 1 to 4 and 27 to 30 of the     framework 1 sequences, reference is also made to the comments made     below. Thus, for determining the degree of amino acid identity,     these residues are preferably disregarded);     and in which:

preferably one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to the Kabat numbering are chosen from the Hallmark residues mentioned in Table A-3 below.

In these Nanobodies, the CDR sequences are generally as further defined herein.

Again, such Nanobodies may be derived in any suitable manner and from any suitable source, and may for example be naturally occurring V_(HH) sequences (i.e. from a suitable species of Camelid) or synthetic or semi-synthetic amino acid sequences, including but not limited to “humanized” (as defined herein) Nanobodies, “camelized” (as defined herein) immunoglobulin sequences (and in particular camelized heavy chain variable domain sequences), as well as Nanobodies that have been obtained by techniques such as affinity maturation (for example, starting from synthetic, random or naturally occurring immunoglobulin sequences), CDR grafting, veneering, combining fragments derived from different immunoglobulin sequences, PCR assembly using overlapping primers, and similar techniques for engineering immunoglobulin sequences well known to the skilled person; or any suitable combination of any of the foregoing as further described herein. Also, when a Nanobody comprises a V_(HH) sequence, said Nanobody may be suitably humanized, as further described herein, so as to provide one or more further (partially or fully) humanized Nanobodies of the invention. Similarly, when a Nanobody comprises a synthetic or semi-synthetic sequence (such as a partially humanized sequence), said Nanobody may optionally be further suitably humanized, again as described herein, again so as to provide one or more further (partially or fully) humanized Nanobodies of the invention.

In particular, humanized Nanobodies may be amino acid sequences that are as generally defined for Nanobodies in the previous paragraphs, but in which at least one amino acid residue is present (and in particular, in at least one of the framework residues) that is and/or that corresponds to a humanizing substitution (as defined herein). Some preferred, but non-limiting humanizing substitutions (and suitable combinations thereof) will become clear to the skilled person based on the disclosure herein. In addition, or alternatively, other potentially useful humanizing substitutions can be ascertained by comparing the sequence of the framework regions of a naturally occurring V_(HH) sequence with the corresponding framework sequence of one or more closely related human V_(H) sequences, after which one or more of the potentially useful humanizing substitutions (or combinations thereof) thus determined can be introduced into said V_(HH) sequence (in any manner known per se, as further described herein) and the resulting humanized V_(HH) sequences can be tested for affinity for the target, for stability, for ease and level of expression, and/or for other desired properties. In this way, by means of a limited degree of trial and error, other suitable humanizing substitutions (or suitable combinations thereof) can be determined by the skilled person based on the disclosure herein. Also, based on the foregoing, (the framework regions of) a Nanobody may be partially humanized or fully humanized.

Some particularly preferred humanized Nanobodies of the invention are humanized variants of the Nanobodies of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239.

Thus, some other preferred Nanobodies of the invention are Nanobodies which can bind (as further defined herein) to human CXCR4 and which:

-   i) are a humanized variant of one of the amino acid sequences of SEQ     ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO:     239; and/or -   ii) have at least 80% amino acid identity with at least one of the     amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ     ID NO: 238 and SEQ ID NO: 239, in which for the purposes of     determining the degree of amino acid identity, the amino acid     residues that form the CDR sequences are disregarded;     and in which: -   i) preferably one or more of the amino acid residues at positions     11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to the Kabat     numbering are chosen from the Hallmark residues mentioned in Table     A-3 below.

Some other preferred Nanobodies of the invention are Nanobodies which can bind (as further defined herein) to human CD4 and which:

-   i) are a humanized variant of one of the amino acid sequences of SEQ     ID NO's: 308 to 311, more preferably SEQ ID NO: 311; and/or -   ii) have at least 80% amino acid identity with at least one of the     amino acid sequences of SEQ ID NO's: 308 to 311, more preferably SEQ     ID NO: 311, in which for the purposes of determining the degree of     amino acid identity, the amino acid residues that form the CDR     sequences are disregarded;     and in which: -   i) preferably one or more of the amino acid residues at positions     11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to the Kabat     numbering are chosen from the Hallmark residues mentioned in Table     A-3 below.

According to another specific aspect of the invention, the invention provides a number of stretches of amino acid residues (i.e. small peptides) that are particularly suited for binding to Targets of the invention. These stretches of amino acid residues may be present in, and/or may be incorporated into, an amino acid sequence of the invention, in particular in such a way that they form (part of) the antigen binding site of an amino acid sequence of the invention. As these stretches of amino acid residues were first generated as CDR sequences of heavy chain antibodies or V_(HH) sequences that were raised against Targets of the invention (or may be based on and/or derived from such CDR sequences, as further described herein), they will also generally be referred to herein as “CDR sequences” (i.e. as CDR1 sequences, CDR2 sequences and CDR3 sequences, respectively). It should however be noted that the invention in its broadest sense is not limited to a specific structural role or function that these stretches of amino acid residues may have in an amino acid sequence of the invention, as long as these stretches of amino acid residues allow the amino acid sequence of the invention to bind to Targets of the invention. Thus, generally, the invention in its broadest sense comprises any amino acid sequence that is capable of binding to Targets of the invention and that comprises one or more CDR sequences as described herein, and in particular a suitable combination of two or more such CDR sequences, that are suitably linked to each other via one or more further amino acid sequences, such that the entire amino acid sequence forms a binding domain and/or binding unit that is capable of binding to Targets of the invention. It should however also be noted that the presence of only one such CDR sequence in an amino acid sequence of the invention may by itself already be sufficient to provide an amino acid sequence of the invention that is capable of binding to Targets of the invention; reference is for example again made to the so-called “Expedite fragments” described in WO 03/050531.

Thus, in another specific, but non-limiting aspect, the amino acid sequence of the invention may be an amino acid sequence that comprises at least one amino acid sequence that is chosen from the group consisting of the CDR1 sequences. CDR2 sequences and CDR3 sequences that are described herein (or any suitable combination thereof). In particular, an amino acid sequence of the invention may be an amino acid sequence that comprises at least one antigen binding site, wherein said antigen binding site comprises at least one amino acid sequence that is chosen from the group consisting of the CDR1 sequences, CDR2 sequences and CDR3 sequences that are described herein (or any suitable combination thereof).

Generally, in this aspect of the invention, the amino acid sequence of the invention may be any amino acid sequence that comprises at least one stretch of amino acid residues, in which said stretch of amino acid residues has an amino acid sequence that corresponds to the sequence of at least one of the CDR sequences described herein. Such an amino acid sequence may or may not comprise an immunoglobulin fold. For example, and without limitation, such an amino acid sequence may be a suitable fragment of an immunoglobulin sequence that comprises at least one such CDR sequence, but that is not large enough to form a (complete) immunoglobulin fold (reference is for example again made to the “Expedite fragments” described in WO 03/050531). Alternatively, such an amino acid sequence may be a suitable “protein scaffold” that comprises least one stretch of amino acid residues that corresponds to such a CDR sequence (i.e. as part of its antigen binding site). Suitable scaffolds for presenting amino acid sequences will be clear to the skilled person, and for example comprise, without limitation, to binding scaffolds based on or derived from immunoglobulins (i.e. other than the immunoglobulin sequences already described herein), protein scaffolds derived from protein A domains (such as Affibodies™), tendamistat, fibronectin, lipocalin, CTLA-4, T-cell receptors, designed ankyrin repeats, avimers and PDZ domains (Binz et al., Nat. Biotech 2005, Vol 23:1257), and binding moieties based on DNA or RNA including but not limited to DNA or RNA aptamers (Ulrich et al., Comb Chem High Throughput Screen 2006 9(8):619-32).

Again, any amino acid sequence of the invention that comprises one or more of these CDR sequences is preferably such that it can specifically bind (as defined herein) to Targets of the invention, and more in particular such that it can bind to Targets of the invention with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein), that is as defined herein.

More in particular, the amino acid sequences according to this aspect of the invention may be any amino acid sequence that comprises at least one antigen binding site, wherein said antigen binding site comprises at least two amino acid sequences that are chosen from the group consisting of the CDR1 sequences described herein, the CDR2 sequences described herein and the CDR3 sequences described herein, such that (i) when the first amino acid sequence is chosen from the CDR1 sequences described herein, the second amino acid sequence is chosen from the CDR2 sequences described herein or the CDR3 sequences described herein; (ii) when the first amino acid sequence is chosen from the CDR2 sequences described herein, the second amino acid sequence is chosen from the CDR1 sequences described herein or the CDR3 sequences described herein; or (iii) when the first amino acid sequence is chosen from the CDR3 sequences described herein, the second amino acid sequence is chosen from the CDR1 sequences described herein or the CDR3 sequences described herein.

Even more in particular, the amino acid sequences of the invention may be amino acid sequences that comprise at least one antigen binding site, wherein said antigen binding site comprises at least three amino acid sequences that are chosen from the group consisting of the CDR1 sequences described herein, the CDR2 sequences described herein and the CDR3 sequences described herein, such that the first amino acid sequence is chosen from the CDR1 sequences described herein, the second amino acid sequence is chosen from the CDR2 sequences described herein, and the third amino acid sequence is chosen from the CDR3 sequences described herein. Preferred combinations of CDR1, CDR2 and CDR3 sequences will become clear from the further description herein. As will be clear to the skilled person, such an amino acid sequence is preferably an immunoglobulin sequence (as further described herein), but it may for example also be any other amino acid sequence that comprises a suitable scaffold for presenting said CDR sequences.

Thus, in one specific, but non-limiting aspect, the invention relates to an amino acid sequence directed against hCXCR4, that comprises one or more stretches of amino acid residues chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207;     or any suitable combination thereof.

When an amino acid sequence of the invention contains one or more amino acid sequences according to b) and/or c):

-   i) any amino acid substitution in such an amino acid sequence     according to b) and/or c) is preferably, and compared to the     corresponding amino acid sequence according to a), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to b) and/or c) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to a);     and/or -   iii) the amino acid sequence according to b) and/or c) may be an     amino acid sequence that is derived from an amino acid sequence     according to a) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

Similarly, when an amino acid sequence of the invention contains one or more amino acid sequences according to e) and/or f):

-   i) any amino acid substitution in such an amino acid sequence     according to e) and/or f) is preferably, and compared to the     corresponding amino acid sequence according to d), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to e) and/or f) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to d);     and/or -   iii) the amino acid sequence according to e) and/or f) may be an     amino acid sequence that is derived from an amino acid sequence     according to d) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

Also, similarly, when an amino acid sequence of the invention contains one or more amino acid sequences according to h) and/or i):

-   i) any amino acid substitution in such an amino acid sequence     according to h) and/or i) is preferably, and compared to the     corresponding amino acid sequence according to g), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to h) and/or i) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to g);     and/or -   iii) the amino acid sequence according to h) and/or i) may be an     amino acid sequence that is derived from an amino acid sequence     according to g) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

It should be understood that the last preceding paragraphs also generally apply to any amino acid sequences of the invention that comprise one or more amino acid sequences according to b), c), e), f), h) or i), respectively.

In this specific aspect, the amino acid sequence preferably comprises one or more stretches of amino acid residues chosen from the group consisting of:

-   i) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   ii) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; and -   iii) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207; or any suitable combination thereof.

Also, preferably, in such an amino acid sequence, at least one of said stretches of amino acid residues forms part of the antigen binding site for binding against hCXCR4.

In a more specific, but again non-limiting aspect, the invention relates to an amino acid sequence directed against hCXCR4 that comprises two or more stretches of amino acid residues chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207;     such that (i) when the first stretch of amino acid residues     corresponds to one of the amino acid sequences according to a), b)     or c), the second stretch of amino acid residues corresponds to one     of the amino acid sequences according to d), e), g), h) or i); (ii)     when the first stretch of amino acid residues corresponds to one of     the amino acid sequences according to d), e) or f), the second     stretch of amino acid residues corresponds to one of the amino acid     sequences according to a), b), c), g), h) or i); or (iii) when the     first stretch of amino acid residues corresponds to one of the amino     acid sequences according to g), h) or i), the second stretch of     amino acid residues corresponds to one of the amino acid sequences     according to a), b), c), d), e) or f).

In this specific aspect, the amino acid sequence preferably comprises two or more stretches of amino acid residues chosen from the group consisting of:

-   i) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   ii) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; and -   iii) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207;     such that, (i) when the first stretch of amino acid residues     corresponds to one of the amino acid sequences of SEQ ID NO's: 142     to 157, more preferably 142 to 143, the second stretch of amino acid     residues corresponds to one of the amino acid sequences of SEQ ID     NO's: 174 to 189, more preferably 174 to 175 or of SEQ ID NO's: 206     to 221, more preferably 206 to 207; (ii) when the first stretch of     amino acid residues corresponds to one of the amino acid sequences     of SEQ ID NO's: 174 to 189, more preferably 174 to 175, the second     stretch of amino acid residues corresponds to one of the amino acid     sequences of SEQ ID NO's: 142 to 157, more preferably 142 to 143 or     of SEQ ID NO's: 206 to 221, more preferably 206 to 207; or (iii)     when the first stretch of amino acid residues corresponds to one of     the amino acid sequences of SEQ ID NO's: 206 to 221, more preferably     206 to 207, the second stretch of amino acid residues corresponds to     one of the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143 or of SEQ ID NO's: 174 to 189, more preferably     174 to 175.

Also, in such an amino acid sequence, the at least two stretches of amino acid residues again preferably form part of the antigen binding site for binding against hCXCR4.

In an even more specific, but non-limiting aspect, the invention relates to an amino acid sequence directed against hCXCR4, that comprises three or more stretches of amino acid residues, in which the first stretch of amino acid residues is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143;     the second stretch of amino acid residues is chosen from the group     consisting of: -   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175;     and the third stretch of amino acid residues is chosen from the     group consisting of: -   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207.

Preferably, in this specific aspect, the first stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 142 to 157, more preferably 142 to 143; the second stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 174 to 189, more preferably 174 to 175; and the third stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 206 to 221, more preferably 206 to 207.

Again, preferably, in such an amino acid sequence, the at least three stretches of amino acid residues forms part of the antigen binding site for binding against hCXCR4.

Preferred combinations of such stretches of amino acid sequences will become clear from the further disclosure herein.

Preferably, in such amino acid sequences the CDR sequences have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said amino acid sequence and one or more of the sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239, in which the amino acid residues that form the framework regions are disregarded. Also, such amino acid sequences of the invention can be as further described herein.

Also, such amino acid sequences are preferably such that they can specifically bind (as defined herein) to hCXCR4; and more in particular bind to hCXCR4 with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on-rate) and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

When the amino acid sequence of the invention essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), the amino acid sequence of the invention is preferably such that:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143;     and/or

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175;     and/or

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207.

In particular, such an amino acid sequence of the invention may be such that CDR1 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 142 to 157, more preferably 142 to 143; and/or CDR2 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 174 to 189, more preferably 174 to 175; and/or CDR3 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 206 to 221, more preferably 206 to 207.

In particular, when the amino acid sequence of the invention essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), the amino acid sequence of the invention is preferably such that:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143;     and

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175;     and

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207; or any suitable fragment of such an     amino acid sequence

In particular, such an amino acid sequence of the invention may be such that CDR1 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 142 to 157, more preferably 142 to 143; and CDR2 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 174 to 189, more preferably 174 to 175; and CDR3 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 206 to 221, more preferably 206 to 207.

Again, preferred combinations of CDR sequences will become clear from the further description herein.

Also, such amino acid sequences are preferably such that they can specifically bind (as defined herein) to hCXCR4; and more in particular bind to hCXCR4 with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

In one preferred, but non-limiting aspect, the invention relates to an amino acid sequence that essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which the CDR sequences of said amino acid sequence have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said amino acid sequence and one or more of the sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239, in which the amino acid residues that form the framework regions are disregarded. Such amino acid sequences of the invention can be as further described herein.

In an even more specific, but non-limiting aspect, the invention relates to an amino acid sequence directed against human CXCR4 able to block CXCL12/SDF1-dependent activation of human CXCR4 (such as a Nanobody of the invention, as further described herein), that comprises one or more stretches of amino acid residues chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143; -   d) the amino acid sequences of SEQ ID NO's: 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175; -   g) the amino acid sequences of SEQ ID NO's: 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207;     or any suitable combination thereof.

When an amino acid sequence of the invention contains one or more amino acid sequences according to b) and/or c):

-   i) any amino acid substitution in such an amino acid sequence     according to b) and/or c) is preferably, and compared to the     corresponding amino acid sequence according to a), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to b) and/or c) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to a);     and/or -   iii) the amino acid sequence according to b) and/or c) may be an     amino acid sequence that is derived from an amino acid sequence     according to a) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

Similarly, when an amino acid sequence of the invention contains one or more amino acid sequences according to e) and/or f):

-   i) any amino acid substitution in such an amino acid sequence     according to e) and/or f) is preferably, and compared to the     corresponding amino acid sequence according to d), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to e) and/or f) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to d);     and/or -   iii) the amino acid sequence according to e) and/or f) may be an     amino acid sequence that is derived from an amino acid sequence     according to d) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

Also, similarly, when an amino acid sequence of the invention contains one or more amino acid sequences according to h) and/or i):

-   i) any amino acid substitution in such an amino acid sequence     according to h) and/or i) is preferably, and compared to the     corresponding amino acid sequence according to g), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to h) and/or i) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to g);     and/or -   iii) the amino acid sequence according to h) and/or i) may be an     amino acid sequence that is derived from an amino acid sequence     according to g) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

It should be understood that the last preceding paragraphs also generally apply to any amino acid sequences of the invention that comprise one or more amino acid sequences according to b), c), e), f), h) or i), respectively.

In this specific aspect, the amino acid sequence preferably comprises one or more stretches of amino acid residues chosen from the group consisting of:

a) the amino acid sequences of SEQ ID NO's: 142 to 143; b) the amino acid sequences of SEQ ID NO's: 174 to 175; and c) the amino acid sequences of SEQ ID NO's: 206 to 207; or any suitable combination thereof.

Also, preferably, in such an amino acid sequence, at least one of said stretches of amino acid residues forms part of the antigen binding site for binding against HUMAN CXCR4.

In a more specific, but again non-limiting aspect, the invention relates to an amino acid sequence directed against human CXCR4, that comprises two or more stretches of amino acid residues chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143; -   d) the amino acid sequences of SEQ ID NO's: 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175; -   g) the amino acid sequences of SEQ ID NO's: 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207;     such that (i) when the first stretch of amino acid residues     corresponds to one of the amino acid sequences according to a), b)     or c), the second stretch of amino acid residues corresponds to one     of the amino acid sequences according to d), e), f), g), h) or     i); (ii) when the first stretch of amino acid residues corresponds     to one of the amino acid sequences according to d), e) or f), the     second stretch of amino acid residues corresponds to one of the     amino acid sequences according to a), b), c), g), h) or i); or (iii)     when the first stretch of amino acid residues corresponds to one of     the amino acid sequences according to g), h) or i), the second     stretch of amino acid residues corresponds to one of the amino acid     sequences according to a), b), c), d), e) or f).

In this specific aspect, the amino acid sequence preferably comprises two or more stretches of amino acid residues chosen from the group consisting of:

a) the amino acid sequences of SEQ ID NO's: 142 to 143; b) the amino acid sequences of SEQ ID NO's: 174 to 175; and c) the amino acid sequences of SEQ ID NO's: 206 to 207; such that, (i) when the first stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 142 to 143, the second stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 174 to 175 or of SEQ ID NO's: 206 to 207; (ii) when the first stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 174 to 175, the second stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 142 to 143 or of SEQ ID NO's: 206 to 207; or (iii) when the first stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 206 to 207, the second stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 142 to 143 or of SEQ ID NO's: 174 to 175.

Also, in such an amino acid sequence, the at least two stretches of amino acid residues again preferably form part of the antigen binding site for binding against human CXCR4.

In an even more specific, but non-limiting aspect, the invention relates to an amino acid sequence directed against human CXCR4, that comprises three or more stretches of amino acid residues, in which the first stretch of amino acid residues is chosen from the group consisting of

-   a) the amino acid sequences of SEQ ID NO's: 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143;     the second stretch of amino acid residues is chosen from the group     consisting of: -   d) the amino acid sequences of SEQ ID NO's: 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175;     and the third stretch of amino acid residues is chosen from the     group consisting of: -   g) the amino acid sequences of SEQ ID NO's: 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207.

Preferably, in this specific aspect, the first stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 142 to 143; the second stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 174 to 175; and the third stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 206 to 207.

Again, preferably, in such an amino acid sequence, the at least three stretches of amino acid residues forms part of the antigen binding site for binding against human CXCR4.

Preferred combinations of such stretches of amino acid sequences will become clear from the further disclosure herein.

Preferably, in such amino acid sequences the CDR sequences have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 238 to 239. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said amino acid sequence and one or more of the sequences of SEQ ID NO's: 238 to 239, in which the amino acid residues that form the framework regions are disregarded. Also, such amino acid sequences of the invention can be as further described herein.

Also, such amino acid sequences are preferably such that they can specifically bind (as defined herein) to human CXCR4; and more in particular bind to human CXCR4 with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

When the amino acid sequence of the invention essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), the amino acid sequence of the invention is preferably such that:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143;     and/or

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175;     and/or

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207.

In particular, such an amino acid sequence of the invention may be such that CDR1 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 142 to 143; and/or CDR2 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 174 to 175; and/or CDR3 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 206 to 207.

In particular, when the amino acid sequence of the invention essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), the amino acid sequence of the invention is preferably such that:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     143;     and

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     175;     and

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     207; or any suitable fragment of such an amino acid sequence

In particular, such an amino acid sequence of the invention may be such that CDR1 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 142 to 143; and CDR2 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 174 to 175; and CDR3 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 206 to 207.

Again, preferred combinations of CDR sequences will become clear from the further description herein.

Also, such amino acid sequences are preferably such that they can specifically bind (as defined herein) to human CXCR4; and more in particular bind to human CXCR4 with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

In one preferred, but non-limiting aspect, the invention relates to an amino acid sequence that essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which the CDR sequences of said amino acid sequence have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 238 to 239. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said amino acid sequence and one or more of the sequences of SEQ ID NO's: 238 to 239, in which the amino acid residues that form the framework regions are disregarded. Such amino acid sequences of the invention can be as further described herein.

Thus, in another specific, but non-limiting aspect, the invention relates to an amino acid sequence directed against hCD4, that comprises one or more stretches of amino acid residues chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more     preferably 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more     preferably 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more     preferably 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303;     or any suitable combination thereof.

When an amino acid sequence of the invention contains one or more amino acid sequences according to b) and/or c):

-   i) any amino acid substitution in such an amino acid sequence     according to b) and/or c) is preferably, and compared to the     corresponding amino acid sequence according to a), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to b) and/or c) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to a);     and/or -   iii) the amino acid sequence according to b) and/or c) may be an     amino acid sequence that is derived from an amino acid sequence     according to a) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

Similarly, when an amino acid sequence of the invention contains one or more amino acid sequences according to e) and/or f):

-   i) any amino acid substitution in such an amino acid sequence     according to e) and/or f) is preferably, and compared to the     corresponding amino acid sequence according to d), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to e) and/or f) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to d);     and/or -   iii) the amino acid sequence according to e) and/or f) may be an     amino acid sequence that is derived from an amino acid sequence     according to d) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

Also, similarly, when an amino acid sequence of the invention contains one or more amino acid sequences according to h) and/or i):

-   i) any amino acid substitution in such an amino acid sequence     according to h) and/or i) is preferably, and compared to the     corresponding amino acid sequence according to g), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to h) and/or i) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to g);     and/or -   iii) the amino acid sequence according to h) and/or i) may be an     amino acid sequence that is derived from an amino acid sequence     according to g) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

It should be understood that the last preceding paragraphs also generally apply to any amino acid sequences of the invention that comprise one or more amino acid sequences according to b), c), e), f), h) or i), respectively.

In this specific aspect, the amino acid sequence preferably comprises one or more stretches of amino acid residues chosen from the group consisting of:

i) the amino acid sequences of SEQ ID NO's: 284 to 287, more preferably 287; ii) the amino acid sequences of SEQ ID NO's: 292 to 295, more preferably 295; and iii) the amino acid sequences of SEQ ID NO's: 300 to 303, more preferably 303; or any suitable combination thereof.

Also, preferably, in such an amino acid sequence, at least one of said stretches of amino acid residues forms part of the antigen binding site for binding against hCD4.

In a more specific, but again non-limiting aspect, the invention relates to an amino acid sequence directed against hCD4 that comprises two or more stretches of amino acid residues chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more     preferably 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more     preferably 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more     preferably 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO s: 300 to     303, more preferably 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303;     such that (i) when the first stretch of amino acid residues     corresponds to one of the amino acid sequences according to a), b)     or c), the second stretch of amino acid residues corresponds to one     of the amino acid sequences according to d), e), f), g), h) or     i); (ii) when the first stretch of amino acid residues corresponds     to one of the amino acid sequences according to d), e) or f), the     second stretch of amino acid residues corresponds to one of the     amino acid sequences according to a), b), c), g), h) or i); or (iii)     when the first stretch of amino acid residues corresponds to one of     the amino acid sequences according to g), h) or i), the second     stretch of amino acid residues corresponds to one of the amino acid     sequences according to a), b), c), d), e) or f).

In this specific aspect, the amino acid sequence preferably comprises two or more stretches of amino acid residues chosen from the group consisting of:

i) the amino acid sequences of SEQ ID NO's: 284 to 287, more preferably 287; ii) the amino acid sequences of SEQ ID NO's: 292 to 295, more preferably 295; and iii) the amino acid sequences of SEQ ID NO's: 300 to 303, more preferably 303; such that, (i) when the first stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 284 to 287, more preferably 287, the second stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 292 to 295, more preferably 295 or of SEQ ID NO's: 300 to 303, more preferably 303; (ii) when the first stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 292 to 295, more preferably 295, the second stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 284 to 287, more preferably 287 or of SEQ ID NO's: 300 to 303, more preferably 303; or (iii) when the first stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 300 to 303, more preferably 303, the second stretch of amino acid residues corresponds to one of the amino acid sequences of SEQ ID NO's: 284 to 287, more preferably 287 or of SEQ ID NO's: 292 to 295, more preferably 295.

Also, in such an amino acid sequence, the at least two stretches of amino acid residues again preferably form part of the antigen binding site for binding against hCD4.

In an even more specific, but non-limiting aspect, the invention relates to an amino acid sequence directed against hCD4, that comprises three or more stretches of amino acid residues, in which the first stretch of amino acid residues is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more     preferably 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287;     the second stretch of amino acid residues is chosen from the group     consisting of -   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more     preferably 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295;     and the third stretch of amino acid residues is chosen from the     group consisting of: -   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more     preferably 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303.

Preferably, in this specific aspect, the first stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 284 to 287, more preferably 287; the second stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 292 to 295, more preferably 295; and the third stretch of amino acid residues is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 300 to 303, more preferably 303.

Again, preferably, in such an amino acid sequence, the at least three stretches of amino acid residues forms part of the antigen binding site for binding against hCD4.

Preferred combinations of such stretches of amino acid sequences will become clear from the further disclosure herein.

Preferably, in such amino acid sequences the CDR sequences have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said amino acid sequence and one or more of the sequences of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311, in which the amino acid residues that form the framework regions are disregarded. Also, such amino acid sequences of the invention can be as further described herein.

Also, such amino acid sequences are preferably such that they can specifically bind (as defined herein) to hCD4; and more in particular bind to hCD4 with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

When the amino acid sequence of the invention essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), the amino acid sequence of the invention is preferably such that:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more     preferably 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287;     and/or

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more     preferably 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295;     and/or

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more     preferably 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303.

In particular, such an amino acid sequence of the invention may be such that CDR1 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 284 to 287, more preferably 287; and/or CDR2 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 292 to 295, more preferably 295; and/or CDR3 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 300 to 303, more preferably 303.

In particular, when the amino acid sequence of the invention essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), the amino acid sequence of the invention is preferably such that:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more     preferably 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287;     and

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more     preferably 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295;     and

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more     preferably 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303; or any suitable fragment of such an amino     acid sequence

In particular, such an amino acid sequence of the invention may be such that CDR1 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 284 to 287, more preferably 287; and CDR2 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 292 to 295, more preferably 295; and CDR3 is chosen from the group consisting of the amino acid sequences of SEQ ID NO's: 300 to 303, more preferably 303.

Again, preferred combinations of CDR sequences will become clear from the further description herein.

Also, such amino acid sequences are preferably such that they can specifically bind (as defined herein) to hCD4; and more in particular bind to hCD4 with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

In one preferred, but non-limiting aspect, the invention relates to an amino acid sequence that essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which the CDR sequences of said amino acid sequence have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said amino acid sequence and one or more of the sequences of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311, in which the amino acid residues that form the framework regions are disregarded. Such amino acid sequences of the invention can be as further described herein.

In an even more specific, but non-limiting aspect, the invention relates to an amino acid sequence directed against human CD4 able to block gp120 binding to CD4 (such as a Nanobody of the invention, as further described herein), that comprises one or more stretches of amino acid residues chosen from the group consisting of:

-   a) the amino acid sequence of SEQ ID NO's: 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 287; -   d) the amino acid sequence of SEQ ID NO: 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 295; -   g) the amino acid sequence of SEQ ID NO: 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 303;     or any suitable combination thereof.

When an amino acid sequence of the invention contains one or more amino acid sequences according to b) and/or c):

-   i) any amino acid substitution in such an amino acid sequence     according to b) and/or c) is preferably, and compared to the     corresponding amino acid sequence according to a), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to b) and/or c) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to a);     and/or -   iii) the amino acid sequence according to b) and/or c) may be an     amino acid sequence that is derived from an amino acid sequence     according to a) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

Similarly, when an amino acid sequence of the invention contains one or more amino acid sequences according to e) and/or f):

-   i) any amino acid substitution in such an amino acid sequence     according to e) and/or f) is preferably, and compared to the     corresponding amino acid sequence according to d), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to e) and/or f) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to d);     and/or -   iii) the amino acid sequence according to e) and/or f) may be an     amino acid sequence that is derived from an amino acid sequence     according to d) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

Also, similarly, when an amino acid sequence of the invention contains one or more amino acid sequences according to h) and/or i):

-   i) any amino acid substitution in such an amino acid sequence     according to h) and/or i) is preferably, and compared to the     corresponding amino acid sequence according to g), a conservative     amino acid substitution, (as defined herein);     and/or -   ii) the amino acid sequence according to h) and/or i) preferably     only contains amino acid substitutions, and no amino acid deletions     or insertions, compared to the corresponding amino acid sequence     according to g);     and/or -   iii) the amino acid sequence according to h) and/or i) may be an     amino acid sequence that is derived from an amino acid sequence     according to g) by means of affinity maturation using one or more     techniques of affinity maturation known per se.

It should be understood that the last preceding paragraphs also generally apply to any amino acid sequences of the invention that comprise one or more amino acid sequences according to b), c), e), f), h) or i), respectively.

In this specific aspect, the amino acid sequence preferably comprises one or more stretches of amino acid residues chosen from the group consisting of:

a) the amino acid sequence of SEQ ID NO: 287; b) the amino acid sequence of SEQ ID NO: 295; and c) the amino acid sequence of SEQ ID NO: 303; or any suitable combination thereof.

Also, preferably, in such an amino acid sequence, at least one of said stretches of amino acid residues forms part of the antigen binding site for binding against hCD4.

In a more specific, but again non-limiting aspect, the invention relates to an amino acid sequence directed against human CD4, that comprises two or more stretches of amino acid residues chosen from the group consisting of:

-   a) the amino acid sequence of SEQ ID NO: 287; -   b) amino acid sequence that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 287; -   d) the amino acid sequences of SEQ ID NO's: 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 295; -   g) the amino acid sequences of SEQ ID NO: 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 303;     such that (i) when the first stretch of amino acid residues     corresponds to one of the amino acid sequences according to a), b)     or c), the second stretch of amino acid residues corresponds to one     of the amino acid sequences according to d), e), f), g), h) or     i); (ii) when the first stretch of amino acid residues corresponds     to one of the amino acid sequences according to d), e) or f), the     second stretch of amino acid residues corresponds to one of the     amino acid sequences according to a), b), c), g), h) or i); or (iii)     when the first stretch of amino acid residues corresponds to one of     the amino acid sequences according to g), h) or i), the second     stretch of amino acid residues corresponds to one of the amino acid     sequences according to a), b), c), d), e) or f).

In this specific aspect, the amino acid sequence preferably comprises two or more stretches of amino acid residues chosen from the group consisting of:

d) the amino acid sequence of SEQ ID NO: 287; e) the amino acid sequence of SEQ ID NO: 295; and f) the amino acid sequence of SEQ ID NO: 303; such that, (i) when the first stretch of amino acid residues corresponds to the amino acid sequence of SEQ ID NO: 287, the second stretch of amino acid residues corresponds to the amino acid sequence of SEQ ID NO: 295 or of SEQ ID NO: 303; (ii) when the first stretch of amino acid residues corresponds to the amino acid sequence of SEQ ID NO: 295, the second stretch of amino acid residues corresponds to the amino acid sequence of SEQ ID NO: 287 or of SEQ ID NO: 303; or (iii) when the first stretch of amino acid residues corresponds to the amino acid sequence of SEQ ID NO: 303, the second stretch of amino acid residues corresponds to the amino acid sequence of SEQ ID NO: 287 or of SEQ ID NO: 295.

Also, in such an amino acid sequence, the at least two stretches of amino acid residues again preferably form part of the antigen binding site for binding against human CD4.

In an even more specific, but non-limiting aspect, the invention relates to an amino acid sequence directed against human CD4, that comprises three or more stretches of amino acid residues, in which the first stretch of amino acid residues is chosen from the group consisting of:

-   a) the amino acid sequence of SEQ ID NO: 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 287;     the second stretch of amino acid residues is chosen from the group     consisting of: -   d) the amino acid sequence of SEQ ID NO: 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 295;     and the third stretch of amino acid residues is chosen from the     group consisting of: -   g) the amino acid sequence of SEQ ID NO: 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 303.

Preferably, in this specific aspect, the first stretch of amino acid residues is chosen from the amino acid sequence of SEQ ID NO: 287; the second stretch of amino acid residues is chosen from the amino acid sequence of SEQ ID NO: 295; and the third stretch of amino acid residues is chosen from the amino acid sequence of SEQ ID NO: 303.

Again, preferably, in such an amino acid sequence, the at least three stretches of amino acid residues forms part of the antigen binding site for binding against human CD4.

Preferred combinations of such stretches of amino acid sequences will become clear from the further disclosure herein.

Preferably, in such amino acid sequences the CDR sequences have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least the amino acid sequence of SEQ ID NO: 311. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said amino acid sequence and the sequence of SEQ ID NO: 311, in which the amino acid residues that form the framework regions are disregarded. Also, such amino acid sequences of the invention can be as further described herein.

Also, such amino acid sequences are preferably such that they can specifically bind (as defined herein) to human. CD4; and more in particular bind to human CD4 with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

When the amino acid sequence of the invention essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), the amino acid sequence of the invention is preferably such that:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequence of SEQ ID NO: 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 287;     and/or

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequence of SEQ ID NO: 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 295;     and/or

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequence of SEQ ID NO: 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 303.

In particular, such an amino acid sequence of the invention may be such that CDR1 is chosen from the amino acid sequence of SEQ ID NO: 287; and/or CDR2 is chosen from the amino acid sequence of SEQ ID NO: 295; and/or CDR3 is chosen from the amino acid sequence of SEQ ID NO: 303.

In particular, when the amino acid sequence of the invention essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), the amino acid sequence of the invention is preferably such that:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequence of SEQ ID NO: 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 287;     and

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequence of SEQ ID NO: 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 295;     and

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequence of SEQ ID NO: 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least the amino acid sequence of SEQ ID NO: 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least the amino acid sequence of SEQ ID NO: 303; or any     suitable fragment of such an amino acid sequence

In particular, such an amino acid sequence of the invention may be such that CDR1 is chosen from the amino acid sequence of SEQ ID NO: 287; and CDR2 is chosen from the amino acid sequence of SEQ ID NO: 295; and CDR3 is chosen from the amino acid sequence of SEQ ID NO: 303.

Again, preferred combinations of CDR sequences will become clear from the further description herein.

Also, such amino acid sequences are preferably such that they can specifically bind (as defined herein) to human CD4; and more in particular bind to human CD4 with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

In one preferred, but non-limiting aspect, the invention relates to an amino acid sequence that essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which the CDR sequences of said amino acid sequence have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least the amino acid sequence of SEQ ID NO: 311. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said amino acid sequence and the sequence of SEQ ID NO: 311, in which the amino acid residues that form the framework regions are disregarded. Such amino acid sequences of the invention can be as further described herein.

In such an amino acid sequence of the invention, the framework sequences may be any suitable framework sequences, and examples of suitable framework sequences will be clear to the skilled person, for example on the basis the standard handbooks and the further disclosure and prior art mentioned herein.

The framework sequences are preferably (a suitable combination of) immunoglobulin framework sequences or framework sequences that have been derived from immunoglobulin framework sequences (for example, by humanization or camelization). For example, the framework sequences may be framework sequences derived from a light chain variable domain (e.g. a V_(L)-sequence) and/or from a heavy chain variable domain (e.g. a V_(H)-sequence). In one particularly preferred aspect, the framework sequences are either framework sequences that have been derived from a V_(HH)-sequence (in which said framework sequences may optionally have been partially or fully humanized) or are conventional V_(H) sequences that have been camelized (as defined herein).

The framework sequences are preferably such that the amino acid sequence of the invention is a domain antibody (or an amino acid sequence that is suitable for use as a domain antibody); is a single domain antibody (or an amino acid sequence that is suitable for use as a single domain antibody); is a “dAb” (or an amino acid sequence that is suitable for use as a dAb); or is a Nanobody (including but not limited to V_(HH) sequence). Again, suitable framework sequences will be clear to the skilled person, for example on the basis the standard handbooks and the further disclosure and prior art mentioned herein.

In particular, the framework sequences present in the amino acid sequences of the invention may contain one or more of Hallmark residues (as defined herein), such that the amino acid sequence of the invention is a Nanobody. Some preferred, but non-limiting examples of (suitable combinations of) such framework sequences will become clear from the further disclosure herein.

Again, as generally described herein for the amino acid sequences of the invention, it is also possible to use suitable fragments (or combinations of fragments) of any of the foregoing, such as fragments that contain one or more CDR sequences, suitably flanked by and/or linked via one or more framework sequences (for example, in the same order as these CDR's and framework sequences may occur in the full-sized immunoglobulin sequence from which the fragment has been derived). Such fragments may also again be such that they comprise or can form an immunoglobulin fold, or alternatively be such that they do not comprise or cannot form an immunoglobulin fold.

In one specific aspect, such a fragment comprises a single CDR sequence as described herein (and in particular a CDR3 sequence), that is flanked on each side by (part of) a framework sequence (and in particular, part of the framework sequence(s) that, in the immunoglobulin sequence from which the fragment is derived, are adjacent to said CDR sequence. For example, a CDR3 sequence may be preceded by (part of) a FR3 sequence and followed by (part of) a FR4 sequence). Such a fragment may also contain a disulphide bridge, and in particular a disulphide bridge that links the two framework regions that precede and follow the CDR sequence, respectively (for the purpose of forming such a disulphide bridge, cysteine residues that naturally occur in said framework regions may be used, or alternatively cysteine residues may be synthetically added to or introduced into said framework regions). For a further description of these “Expedite fragments”, reference is again made to WO 03/050531, as well as to as well as to WO 08/068280.

In another aspect, the invention relates to a compound or construct, and in particular a protein or polypeptide (also referred to herein as a “compound of the invention” or “polypeptide of the invention”, respectively) that comprises or essentially consists of one or more amino acid sequences of the invention (or suitable fragments thereof), and optionally further comprises one or more other groups, residues, moieties or binding units. As will become clear to the skilled person from the further disclosure herein, such further groups, residues, moieties, binding units or amino acid sequences may or may not provide further functionality to the amino acid sequence of the invention (and/or to the compound or construct in which it is present) and may or may not modify the properties of the amino acid sequence of the invention.

For example, such further groups, residues, moieties or binding units may be one or more additional amino acid sequences, such that the compound or construct is a (fusion) protein or (fusion) polypeptide. In a preferred but non-limiting aspect, said one or more other groups, residues, moieties or binding units are immunoglobulin sequences. Even more preferably, said one or more other groups, residues, moieties or binding units are chosen from the group consisting of domain antibodies, amino acid sequences that are suitable for use as a domain antibody, single domain antibodies, amino acid sequences that are suitable for use as a single domain antibody. “dAb”'s, amino acid sequences that are suitable for use as a dAb, or Nanobodies.

Alternatively, such groups, residues, moieties or binding units may for example be chemical groups, residues, moieties, which may or may not by themselves be biologically and/or pharmacologically active. For example, and without limitation, such groups may be linked to the one or more amino acid sequences of the invention so as to provide a “derivative” of an amino acid sequence or polypeptide of the invention, as further described herein.

The polypeptides of the invention comprise or essentially consist of at least one Nanobody of the invention. Some preferred, but non-limiting examples of polypeptides of the invention are given in SEQ ID NO's: 261 to 264, more preferably SEQ ID NO's 263 to 264.

TABLE 2 Preferred polypeptide or compound sequences (also referred herein as a sequence with a particular name or SEQ ID NO: X, wherein X is a number  referring to the relevant amino acid sequence): Amino Acid Sequence Clone name SEQ ID NO: EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGL 238D2-10GS- 261 EWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPED 238D2 TAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSSGGGGSGGGGSEVQ LVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGLEWV SGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPEDTAV YYCAKSRVSRTGLYTYDNRGQGTQVTVSS EVQLMESGGGLVQAGGSLRLSCAASGRTFNNYAMGWFRRAPGKER 238D4-20GS- 262 EFVAAITRSGVRSGVSAIYGDSVKDRFTISRDNAKNTLYLQMNSL 238D4 KPEDTAVYTCAASAIGSGALRRFEYDYSGQGTQVTVSSGGGGSGG GGSGGGGSGGGGSEVQLMESGGGLVQAGGSLRLSCAASGRTFNNY AMGWFRRAPGKEREFVAAITRSGVRSGVSAIYGDSVKDRFTISRD NAKNTLYLQMNSLKPEDTAVYTCAASAIGSGALRRFEYDYSGQGT QVTVSS EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGL 238D2-15GS- 263 EWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPED 238D4 TAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSSGGGGSGGGGSGGG GSEVQLMESGGGLVQAGGSLRLSCAASGRTFNNYAMGWFRRAPGK EREFVAAITRSGVRSGVSAIYGDSVKDRFTISRDNAKNTLYLQMN SLKPEDTAVYTCAASAIGSGALRRFEYDYSGQGTQVTVSS EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGL 238D2-20GS 264 EWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPED 238D4 TAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSSGGGGSGGGGSGGG GSGGGGSEVQLMESGGGLVQAGGSLRLSCAASGRTFNNYAMGWFR RAPGKEREFVAAITRSGVRSGVSAIYGDSVKDRFTISRDNAKNTL YLQMNSLKPEDTAVYTCAASAIGSGALRRFEYDYSGQGTQVTVSS

Also within the scope of the present invention are compounds or constructs, that comprises or essentially consists of one or more derivatives as described herein, and optionally further comprises one or more other groups, residues, moieties or binding units, optionally linked via one or more linkers. Preferably, said one or more other groups, residues, moieties or binding units are amino acid sequences.

In the compounds or constructs described above, the one or more amino acid sequences of the invention and the one or more groups, residues, moieties or binding units may be linked directly to each other and/or via one or more suitable linkers or spacers. For example, when the one or more groups, residues, moieties or binding units are amino acid sequences, the linkers may also be amino acid sequences, so that the resulting compound or construct is a fusion (protein) or fusion (polypeptide).

The compounds or polypeptides of the invention can generally be prepared by a method which comprises at least one step of suitably linking the one or more amino acid sequences of the invention to the one or more further groups, residues, moieties or binding units, optionally via the one or more suitable linkers, so as to provide the compound or polypeptide of the invention. Polypeptides of the invention can also be prepared by a method which generally comprises at least the steps of providing a nucleic acid that encodes a polypeptide of the invention, expressing said nucleic acid in a suitable manner, and recovering the expressed polypeptide of the invention. Such methods can be performed in a manner known per se, which will be clear to the skilled person, for example on the basis of the methods and techniques further described herein.

The process of designing/selecting and/or preparing a compound or polypeptide of the invention, starting from an amino acid sequence of the invention, is also referred to herein as “formatting” said amino acid sequence of the invention; and an amino acid of the invention that is made part of a compound or polypeptide of the invention is said to be “formatted” or to be “in the format of” said compound or polypeptide of the invention. Examples of ways in which an amino acid sequence of the invention can be formatted and examples of such formats will be clear to the skilled person based on the disclosure herein; and such formatted amino acid sequences form a further aspect of the invention.

In one specific aspect of the invention, a compound of the invention or a polypeptide of the invention may have an increased half-life, compared to the corresponding amino acid sequence of the invention. Some preferred, but non-limiting examples of such compounds and polypeptides will become clear to the skilled person based on the further disclosure herein, and for example comprise amino acid sequences or polypeptides of the invention that have been chemically modified to increase the half-life thereof (for example, by means of pegylation); amino acid sequences of the invention that comprise at least one additional binding site for binding to a serum protein (such as serum albumin; see for example EP 0 368 684 B1, page 4); or polypeptides of the invention that comprise at least one amino acid sequence of the invention that is linked to at least one moiety (and in particular at least one amino acid sequence) that increases the half-life of the amino acid sequence of the invention. Examples of polypeptides of the invention that comprise such half-life extending moieties or amino acid sequences will become clear to the skilled person based on the further disclosure herein; and for example include, without limitation, polypeptides in which the one or more amino acid sequences of the invention are suitable linked to one or more serum proteins or fragments thereof (such as (human) serum albumin or suitable fragments thereof) or to one or more binding units that can bind to serum proteins (such as, for example, domain antibodies, amino acid sequences that are suitable for use as a domain antibody, single domain antibodies, amino acid sequences that are suitable for use as a single domain antibody, “dAb”'s, amino acid sequences that are suitable for use as a dAb, or Nanobodies that can bind to serum proteins such as serum albumin (such as human serum albumin), serum immunoglobulins such as IgG, or transferrin; reference is made to the further description and references mentioned herein); polypeptides in which an amino acid sequence of the invention is linked to an Fc portion (such as a human Fc) or a suitable part or fragment thereof; or polypeptides in which the one or more amino acid sequences of the invention are suitable linked to one or more small proteins or peptides that can bind to serum proteins (such as, without limitation, the proteins and peptides described in WO 91/01743, WO 01/45746, WO 02/076489 and to WO 08/068280.

Generally, the compounds or polypeptides of the invention with increased half-life preferably have a half-life that is at least 1.5 times, preferably at least 2 times, such as at least 5 times, for example at least 10 times or more than 20 times, greater than the half-life of the corresponding amino acid sequence of the invention per se. For example, the compounds or polypeptides of the invention with increased half-life may have a half-life that is increased with more than 1 hours, preferably more than 2 hours, more preferably more than 6 hours, such as more than 12 hours, or even more than 24, 48 or 72 hours, compared to the corresponding amino acid sequence of the invention per se.

In a preferred, but non-limiting aspect of the invention, such compounds or polypeptides of the invention have a serum half-life that is increased with more than 1 hours, preferably more than 2 hours, more preferably more than 6 hours, such as more than 12 hours, or even more than 24, 48 or 72 hours, compared to the corresponding amino acid sequence of the invention per se.

In another preferred, but non-limiting aspect of the invention, such compounds or polypeptides of the invention exhibit a serum half-life in human of at least about 12 hours, preferably at least 24 hours, more preferably at least 48 hours, even more preferably at least 72 hours or more. For example, compounds or polypeptides of the invention may have a half life of at least 5 days (such as about 5 to 10 days), preferably at least 9 days (such as about 9 to 14 days), more preferably at least about 10 days (such as about 10 to 15 days), or at least about 11 days (such as about 11 to 16 days), more preferably at least about 12 days (such as about 12 to 18 days or more), or more than 14 days (such as about 14 to 19 days).

In another aspect, the invention relates to a nucleic acid that encodes an amino acid sequence of the invention or a polypeptide of the invention (or a suitable fragment thereof). Such a nucleic acid will also be referred to herein as a “nucleic acid of the invention” and may for example be in the form of a genetic construct, as further described herein.

In another aspect, the invention relates to a host or host cell that expresses (or that under suitable circumstances is capable of expressing) an amino acid sequence of the invention and/or a polypeptide of the invention; and/or that contains a nucleic acid of the invention. Some preferred but non-limiting examples of such hosts or host cells will become clear from the further description herein.

The invention further relates to a product or composition containing or comprising at least one amino acid sequence of the invention, at least one polypeptide of the invention (or a suitable fragment thereof) and/or at least one nucleic acid of the invention, and optionally one or more further components of such compositions known per se, i.e. depending on the intended use of the composition. Such a product or composition may for example be a pharmaceutical composition (as described herein), a veterinary composition or a product or composition for diagnostic use (as also described herein). Some preferred but non-limiting examples of such products or compositions will become clear from the further description herein.

The invention also relates to the use of an amino acid sequence, Nanobody or polypeptide of the invention, or of a composition comprising the same, in (methods or compositions for) modulating a Target of the invention, either in vitro (e.g. in an in vitro or cellular assay) or in vivo (e.g. in an a single cell or in a multicellular organism, and in particular in a mammal, and more in particular in a human being, such as in a human being that is at risk of or suffers from Targets of the invention related disease or disorder).

The invention also relates to methods for modulating a Target of the invention, either in vitro (e.g. in an in vitro or cellular assay) or in vivo (e.g. in an a single cell or multicellular organism, and in particular in a mammal, and more in particular in a human being, such as in a human being that is at risk of or suffers from Targets of the invention related disease or disorder), which method comprises at least the step of contacting Targets of the invention with at least one amino acid sequence, Nanobody or polypeptide of the invention, or with a composition comprising the same, in a manner and in an amount suitable to modulate Targets of the invention, with at least one amino acid sequence, Nanobody or polypeptide of the invention.

The invention also relates to the use of an one amino acid sequence, Nanobody or polypeptide of the invention in the preparation of a composition (such as, without limitation, a pharmaceutical composition or preparation as further described herein) for modulating Targets of the invention, either in vitro (e.g. in an in vitro or cellular assay) or in vivo (e.g. in an a single cell or multicellular organism, and in particular in a mammal, and more in particular in a human being, such as in a human being that is at risk of or suffers from a Targets of the invention related disease or disorder).

In the context of the present invention, “modulating” or “to modulate” generally means either reducing or inhibiting the activity of, or alternatively increasing the activity of, Targets of the invention, as measured using a suitable in vitro, cellular or in vivo assay (such as those mentioned herein). In particular, “modulating” or “to modulate” may mean either reducing or inhibiting the activity of, or alternatively increasing the activity of, Targets of the invention, as measured using a suitable in vitro, cellular or in vivo assay (such as those mentioned herein), by at least 1%, preferably at least 5%, such as at least 10% or at least 25%, for example by at least 50%, at least 60%, at least 70%, at least 80%, or 90% or more, compared to activity of Targets of the invention in the same assay under the same conditions but without the presence of the amino acid sequence, Nanobody or polypeptide of the invention.

As will be clear to the skilled person, “modulating” may also involve effecting a change (which may either be an increase or a decrease) in affinity, avidity, specificity and/or selectivity of Targets of the invention for one or more of its targets, ligands or substrates; and/or effecting a change (which may either be an increase or a decrease) in the sensitivity of a Target of the invention for one or more conditions in the medium or surroundings in which the Target of the invention is present (such as pH, ion strength, the presence of co-factors, etc.), compared to the same conditions but without the presence of the amino acid sequence, Nanobody or polypeptide of the invention. As will be clear to the skilled person, this may again be determined in any suitable manner and/or using any suitable assay known per se, such as the assays described herein or in the prior art cited herein.

“Modulating” may also mean effecting a change (i.e. an activity as an agonist, as an antagonist or as a reverse agonist, respectively, depending on the Target of the invention and the desired biological or physiological effect) with respect to one or more biological or physiological mechanisms, effects, responses, functions, pathways or activities in which a Target of the invention (or in which its substrate(s), ligand(s) or pathway(s) are involved, such as its signalling pathway or metabolic pathway and their associated biological or physiological effects) is involved. Again, as will be clear to the skilled person, such an action as an agonist or an antagonist may be determined in any suitable manner and/or using any suitable (in vitro and usually cellular or in assay) assay known per se, such as the assays described herein or in the prior art cited herein. In particular, an action as an agonist or antagonist may be such that an intended biological or physiological activity is increased or decreased, respectively, by at least 1%, preferably at least 5%, such as at least 10% or at least 25%, for example by at least 50%, at least 60%, at least 70%, at least 80%, or 90% or more, compared to the biological or physiological activity in the same assay under the same conditions but without the presence of the amino acid sequence, Nanobody or polypeptide of the invention.

Modulating may for example involve allosteric modulation (see for example George et al., Nat Rev Drug Discov 1:808-820 (2002); Kenakin, Trends Pharmacol Sci 25:186-192 (2002) and Rios et al., Pharmacol Ther 92:71-87 (2001)) and/or reducing or inhibiting the binding of a Target of the invention to one of its substrates or ligands and/or competing with a natural ligand, substrate for binding to a Target of the invention. Modulating may also involve activating a Target of the invention or the mechanism or pathway in which it is involved. Modulating may be reversible or irreversible, but for pharmaceutical and pharmacological purposes will usually be in a reversible manner.

The invention further relates to methods for preparing or generating the amino acid sequences, polypeptides, nucleic acids, host cells, products and compositions described herein. Some preferred but non-limiting examples of such methods will become clear from the further description herein.

Generally, these methods may comprise the steps of:

-   a) providing a set, collection or library of amino acid sequences;     and -   b) screening said set, collection or library of amino acid sequences     for amino acid sequences that can bind to and/or have affinity for     Targets of the invention;     and -   c) isolating the amino acid sequence(s) that can bind to and/or have     affinity for Targets of the invention.

In particular, in step b) of such a method, the set, collection or library may be screened for amino acid sequences that can bind to and/or have affinity for Targets of the invention that are expressed on the surface of a suitable cell; for amino acid sequences that can bind to and/or have affinity for an extracellular part, region, domain, loop or other extracellular epitope of a Target of the invention (as described herein); and/or for amino acid sequences that can bind to and/or have affinity for a peptide that has been derived from or based on the amino acid sequence of an extracellular part, region, domain, loop or other extracellular epitope of a Target of the invention. This can be performed using methods and techniques known per se, for example those mentioned herein.

In such a method, the set, collection or library of amino acid sequences may be any suitable set, collection or library of amino acid sequences. For example, the set, collection or library of amino acid sequences may be a set, collection or library of immunoglobulin sequences (as described herein), such as a naïve set, collection or library of immunoglobulin sequences; a synthetic or semi-synthetic set, collection or library of immunoglobulin sequences; and/or a set, collection or library of immunoglobulin sequences that have been subjected to affinity maturation.

Also, in such a method, the set, collection or library of amino acid sequences may be a set, collection or library of heavy chain variable domains (such as V_(H) domains or V_(HH) domains) or of light chain variable domains. For example, the set, collection or library of amino acid sequences may be a set, collection or library of domain antibodies or single domain antibodies, or may be a set, collection or library of amino acid sequences that are capable of functioning as a domain antibody or single domain antibody.

In a preferred aspect of this method, the set, collection or library of amino acid sequences may be an immune set, collection or library of immunoglobulin sequences, for example derived from a mammal that has been suitably immunized with Targets of the invention or with a suitable antigenic determinant based thereon or derived therefrom, such as an antigenic part, fragment, region, domain, loop or other epitope thereof. In one particular aspect, said antigenic determinant may be an extracellular part, region, domain, loop or other extracellular epitope(s), or a suitable peptide derived therefrom. Alternatively, as mentioned herein, the set, collection or library of amino acid sequences may be an immune set, collection or library of immunoglobulin sequences, for example derived from a mammal that has been suitably immunized with a refolded Target of the invention or with a cell, or cell fraction or preparation derived from a cell that has a Target of the invention on its surface.

In the above methods, the set, collection or library of amino acid sequences may be displayed on a phage, phagemid, ribosome or suitable micro-organism (such as yeast), such as to facilitate screening. Suitable methods, techniques and host organisms for displaying and screening (a set, collection or library of) amino acid sequences will be clear to the person skilled in the art, for example on the basis of the further disclosure herein. Reference is also made to the review by Hoogenboom in Nature Biotechnology, 23, 9, 1105-1116 (2005).

In another aspect, the method for generating amino acid sequences comprises at least the steps of:

-   a) providing a collection or sample of cells expressing amino acid     sequences; -   b) screening said collection or sample of cells for cells that     express an amino acid sequence that can bind to and/or have affinity     for Targets of the invention;     and -   c) either (i) isolating said amino acid sequence; or (ii) isolating     from said cell a nucleic acid sequence that encodes said amino acid     sequence, followed by expressing said amino acid sequence.

In particular, in step b) of such a method, the set, collection or library may be screened for cells that express amino acid sequences that can bind to and/or have affinity for Targets of the invention that are expressed on the surface of a suitable cell; for cells that express amino acid sequences that can bind to and/or have affinity for an extracellular part, region, domain, loop or other extracellular epitope of a Target of the invention (as described herein); and/or for cells that express amino acid sequences that can bind to and/or have affinity for a peptide that has been derived from or based on the amino acid sequence of an extracellular part, region, domain, loop or other extracellular epitope of a Target of the invention. This can be performed using methods and techniques known per se, for example those mentioned herein.

For example, when the desired amino acid sequence is an immunoglobulin sequence, the collection or sample of cells may for example be a collection or sample of B-cells. Also, in this method, the sample of cells may be derived from a mammal that has been suitably immunized with Targets of the invention or with a suitable antigenic determinant based thereon or derived therefrom, such as an antigenic part, fragment, region, domain, loop or other epitope thereof. In one particular aspect, said antigenic determinant may be an extracellular part, region, domain, loop or other extracellular epitope(s), or a suitable peptide derived therefrom. Alternatively, as mentioned herein, the sample of cells may be derived from a mammal that has been suitably immunized with a refolded Target of the invention or with a cell, or cell fraction or preparation derived from a cell that has a Target of the invention on its surface.

The above method may be performed in any suitable manner, as will be clear to the skilled person. Reference is for example made to EP 0 542 810, WO 05/19824, WO 04/051268 and WO 04/106377. The screening of step b) is preferably performed using a flow cytometry technique such as FACS. For this, reference is for example made to Lieby et al., Blood, Vol. 97, No. 12, 3820 (2001).

In another aspect, the method for generating an amino acid sequence directed against Targets of the invention may comprise at least the steps of:

-   a) providing a set, collection or library of nucleic acid sequences     encoding amino acid sequences; -   b) screening said set, collection or library of nucleic acid     sequences for nucleic acid sequences that encode an amino acid     sequence that can bind to and/or has affinity for Targets of the     invention;     and -   c) isolating said nucleic acid sequence, followed by expressing said     amino acid sequence.

In particular, in step b) of such a method, the set, collection or library may be screened for nucleotide sequences that encode amino acid sequences that can bind to and/or have affinity for Targets of the invention that are expressed on the surface of a suitable cell; for nucleotide sequences that encode amino acid sequences that can bind to and/or have affinity for an extracellular part, region, domain, loop or other extracellular epitope of a Target of the invention (as described herein); and/or for nucleotide sequences that encode amino acid sequences that can bind to and/or have affinity for a peptide that has been derived from or based on the amino acid sequence of an extracellular part, region, domain, loop or other extracellular epitope of a Target of the invention. This can be performed using methods and techniques known per se, for example those mentioned herein.

In such a method, the set, collection or library of nucleic acid sequences encoding amino acid sequences may for example be a set, collection or library of nucleic acid sequences encoding a naïve set, collection or library of immunoglobulin sequences; a set, collection or library of nucleic acid sequences encoding a synthetic or semi-synthetic set, collection or library of immunoglobulin sequences; and/or a set, collection or library of nucleic acid sequences encoding a set, collection or library of immunoglobulin sequences that have been subjected to affinity maturation.

Also, in such a method, the set, collection or library of nucleic acid sequences may encode a set, collection or library of heavy chain variable domains (such as V_(H) domains or V_(HH) domains) or of light chain variable domains. For example, the set, collection or library of nucleic acid sequences may encode a set, collection or library of domain antibodies or single domain antibodies, or a set, collection or library of amino acid sequences that are capable of functioning as a domain antibody or single domain antibody.

In a preferred aspect of this method, the set, collection or library of nucleic acid sequences may be an immune set, collection or library of nucleic acid sequences, for example derived from a mammal that has been suitably immunized with Targets of the invention or with a suitable antigenic determinant based thereon or derived therefrom, such as an antigenic part, fragment, region, domain, loop or other epitope thereof. In one particular aspect, said antigenic determinant may be an extracellular part, region, domain, loop or other extracellular epitope(s), or a suitable peptide derived therefrom. Alternatively, as mentioned herein, the set, collection or library of nucleic acid sequences may be an immune set, collection or library derived from a mammal that has been suitably immunized with a Target of the invention or with a cell, or cell fraction or preparation derived from a cell that has a Target of the invention on its surface.

The set, collection or library of nucleic acid sequences may for example encode an immune set, collection or library of heavy chain variable domains or of light chain variable domains. In one specific aspect, the set, collection or library of nucleotide sequences may encode a set, collection or library of V_(HH) sequences.

In the above methods, the set, collection or library of nucleotide sequences may be displayed on a phage, phagemid, ribosome or suitable micro-organism (such as yeast), such as to facilitate screening. Suitable methods, techniques and host organisms for displaying and screening (a set, collection or library of) nucleotide sequences encoding amino acid sequences will be clear to the person skilled in the art, for example on the basis of the further disclosure herein. Reference is also made to the review by Hoogenboom in Nature Biotechnology, 23, 9, 1105-1116 (2005).

In another aspect, the method for generating an amino acid sequence directed against hCXCR4 may comprise at least the steps of:

-   a) providing a set, collection or library of nucleic acid sequences     encoding amino acid sequences; -   b) screening said set, collection or library of nucleic acid     sequences for nucleic acid sequences that encode an amino acid     sequence that can bind to and/or has affinity for hCXCR4 and that is     cross-blocked or is cross blocking a Nanobody of the invention, e.g.     SEQ ID NO: 238 to 253 (Table 1), or a polypeptide or construct of     the invention, e.g. SEQ ID NO: 261-266 (see Table 2); and -   c) isolating said nucleic acid sequence, followed by expressing said     amino acid sequence.

In yet another aspect, the method for generating an amino acid sequence directed against hF4 may comprise at least the steps of:

-   a) providing a set, collection or library of nucleic acid sequences     encoding amino acid sequences; -   b) screening said set, collection or library of nucleic acid     sequences for nucleic acid sequences that encode an amino acid     sequence that can bind to and/or has affinity for hCD4 and that is     cross-blocked or is cross blocking a Nanobody of the invention, e.g.     SEQ ID NO: 308 to 311 (Table 3); and -   c) isolating said nucleic acid sequence, followed by expressing said     amino acid sequence.

The invention also relates to amino acid sequences that are obtained by the above methods, or alternatively by a method that comprises the one of the above methods and in addition at least the steps of determining the nucleotide sequence or amino acid sequence of said immunoglobulin sequence; and of expressing or synthesizing said amino acid sequence in a manner known per se, such as by expression in a suitable host cell or host organism or by chemical synthesis.

Also, following the steps above, one or more amino acid sequences of the invention may be suitably humanized (or alternatively camelized); and/or the amino acid sequence(s) thus obtained may be linked to each other or to one or more other suitable amino acid sequences (optionally via one or more suitable linkers) so as to provide a polypeptide of the invention. Also, a nucleic acid sequence encoding an amino acid sequence of the invention may be suitably humanized (or alternatively camelized) and suitably expressed; and/or one or more nucleic acid sequences encoding an amino acid sequence of the invention may be linked to each other or to one or more nucleic acid sequences that encode other suitable amino acid sequences (optionally via nucleotide sequences that encode one or more suitable linkers), after which the nucleotide sequence thus obtained may be suitably expressed so as to provide a polypeptide of the invention.

The invention further relates to applications and uses of the amino acid sequences, compounds, constructs, polypeptides, nucleic acids, host cells, products and compositions described herein, as well as to methods for the prevention and/or treatment for diseases and disorders associated with Targets of the invention. Some preferred but non-limiting applications and uses will become clear from the further description herein.

The invention also relates to the amino acid sequences, compounds, constructs, polypeptides, nucleic acids, host cells, products and compositions described herein for use in therapy.

In particular, the invention also relates to the amino acid sequences, compounds, constructs, polypeptides, nucleic acids, host cells, products and compositions described herein for use in therapy of a disease or disorder that can be prevented or treated by administering, to a subject in need thereof, of (a pharmaceutically effective amount of) an amino acid sequence, compound, construct or polypeptide as described herein.

More in particular, the invention relates to the amino acid sequences, compounds, constructs, polypeptides, nucleic acids, host cells, products and compositions described herein for use in therapy of viral and bacterial induced diseases and/or disorders, such as e.g. AIDS, Hepatitis C, Heptatitis B, adenovirus infection, hantavirus infection, herpesvirus infection, echo-virus infection, etc.

The amino acid sequences, Nanobodies and polypeptides of the invention may also find use as markers for detecting cells that express the Targets of the invention against which they are directed, for example in vitro (e.g. using Western blot, immunoprecipitation or immunofluorescence techniques) or in vivo (e.g. using suitable imaging techniques). The amino acid sequences, Nanobodies and polypeptides of the invention may also find use in affinity purification techniques for (cells expressing) the Targets of the invention against which they are directed.

Other aspects, embodiments, advantages and applications of the invention will also become clear from the further description herein, in which the invention will be described and discussed in more detail with reference to the Nanobodies of the invention and polypeptides of the invention comprising the same, which form some of the preferred aspects of the invention.

As will become clear from the further description herein, Nanobodies generally offer certain advantages (outlined herein) compared to “dAb's” or similar (single) domain antibodies or immunoglobulin sequences, which advantages are also provided by the Nanobodies of the invention. However, it will be clear to the skilled person that the more general aspects of the teaching below can also be applied (either directly or analogously) to other amino acid sequences of the invention.

FIGURES

FIG. 1: Schematic representation of the selection procedure. Abbreviations: CHO-CXCR4: membrane of CHO (Chinese Hamster Ovary) cells transiently transfected with human CXCR4; COS7-CXCR4: membrane of COS7 (Monkey cells) cells transiently transfected with human CXCR4; R1 is first round of selection; R2 is the second round of selection; Counterselection means that the selection was done in the presence of CHO-membrane (non expressing CXCR4); ligand is CXCL12/SDF1 (3 ug in 100 ul PBS), antagonist is AMD3100 (50 uM), antibody is 12G5 (5 ug in 100 ul PBS).

FIG. 2: Results from Phage ELISA (as described in example 1.5), showing that 238C1, 238D2, 238F3 have high specificity toward CXCR4 expressing membrane compared to non-expressing membrane (−).

FIG. 3: Primary and secondary screen of Nanobody clones binding to CXCR4. [¹²⁵I]-CXCL12 competition binding experiments were directly performed with periplasma fractions (1:10) on cell membranes from HEK293T cells transiently expressing CXCR4. All primary hits (A) were confirmed in a second screen (B). Control experiments with AMD3100 (3 μM) or vehicle (−) were performed to show full and no displacement, respectively.

FIG. 4: Competition binding of monovalent Nanobodies and reference ligands to CXCR4. A-C) Competition binding experiments with [¹²⁵I]-CXCL12, [¹²⁵I]-238D2 or [¹²⁵I]-238D4 as radioligand were performed on cell membranes from HEK293T cells transiently expressing CXCR4. Control displacement experiments with AMD3100 (3 μM; AMD), CXCL12 (30 nM; XL12) or vehicle (−) were performed. Data are shown as means±S.E.M (n=2-6). D) Total binding (vehicle; −) and competition binding experiments (3 μM AMD3100; AMD) with [¹²⁵I]-238D2 or [¹²⁵I]-238D4 as radioligand were performed on cell membranes from HEK293T cells transiently expressing CXCR4 or CXCR3. Data are shown as means±S.E.M (n=3).

FIG. 5: The monovalent antibodies 238D2 and 238D4 are potent CXCR4 antagonists. A) Inositol phosphate (IP) accumulation experiments were performed in HEK293T cells transiently expressing CXCR4 and Gα_(qi5). Agonism experiments (left graph) show no intrinsic activity for 238D2 and 238D4. Antagonism experiments (right graph) were performed in the presence of CXCL12 (30 nM) following 1 h pre-incubation with 238D2 or 238D4. Control experiments with vehicle (−) or AMD3100 (3 μM; AMD) were performed. Data are shown as means±S.E.M (n=4). B) Reporter gene experiments were performed in HEK293T cells transiently transfected with pCRE/β-galactosidase and a plasmid encoding CXCR4. No agonist activity for 238D2 and 238D4 was observed (left graph). Data are shown as means±S.E.M (n=3). Experiments showing competitive antagonism of the CXCL12-induced reporter gene activation were performed by establishing concentration response curves for CXCL12 in the presence of increasing concentrations of 238D2 or 238D4 (right graphs). Schild regression analysis graphs are embedded. Data are shown as means±S.E.M (n=4-6). C) Chemotaxis experiments using ChemoTx™ plates were performed with Jurkat cells endogenously expressing CXCR4. Agonism experiments (left graph) show migration of Jurkat cells from the upper compartment towards CXCL12 but not towards 238D2 and 238D4 in the lower compartment of the chemotaxis plate. Experiments showing the inhibition of migration towards CXCL12 (0.3 nM) were performed in the presence of 238D2 or 238D4 in both compartments. Control experiments with AMD3100 (3 μM; AMD) were performed. Data are shown as means±S.E.M (n=4).

FIG. 6: Monoclonals were sequenced and grouped based on their similarity to form families (more than 2 sequences). The clones on the same lane are 100% identical. U=unique sequences non related to each others.

FIG. 7: The monovalent Nanobodies 238D2 and 238D4 do not act as agonists or antagonists on chemokine CCR5, CCR7, CXCR1, CXCR2, CXCR3, CXCR6, β₂ adrenergic and histamine H₄ receptors. The selectivity screen was performed with two concentrations of 238D2 and 238D4 in the presence of a EC₅₀-EC₈₀ of an agonist and in the absence (for the investigation of β₂ adrenoceptors) or the presence of forskolin (3 μM; for the investigation of all other receptors) on HEK293T cells transiently transfected with cDNA encoding the mentioned receptors (or mock for the investigation of endogenously expressed β₂ adrenoceptors) using the CRE/β-galactosidase reporter gene assay. Data are shown as means±S.E.M (n=2-3).

FIG. 8: Bivalent Nanobodies show increased affinity and inhibitory potency compared to their monovalent counterparts. A) Competition binding experiments with [¹²⁵I]-CXCL12 were performed on cell membranes from HEK293T cells transiently expressing CXCR4. Control displacement experiments with AMD3100 (3 μM; AMD), CXCL12 (30 nM; XL12) or vehicle (−) were performed. Data are shown as means±S.E.M (n=2-6). B) Chemotaxis experiments using ChemoTx™ plates were performed with Jurkat cells endogenously expressing CXCR4. Experiments showing the inhibition of migration towards CXCL12 (0.3 nM) in the lower compartment were performed in the presence of Nanobodies in both compartments. Control experiments with AMD3100 (3 μM; AMD) were performed. Data are shown as means±S.E.M (n=3-4).

FIG. 9: CD4 binding assay for a selection of clones. Negative controls are addition of irrelevant phage and no phage addition.

FIG. 10: CD4-gp120 blocking assay for selected Nanobodies. Monoclonal mAb A1 was used as positive control. Negative control was no addition of Nanobody.

FIG. 11: FACS experiment showing the binding of Nanobodies to Jurkat cells expressing CD4. Negative controls—TOPRO, Unstained, anti mouse-PE, anti myc+anti mouse-PE. Positive control—Monoclonal anti CD4 antibody mAb A1.

DETAILED DESCRIPTION OF THE INVENTION

In some embodiments, targets of the invention are human cellular receptors for viruses and/or bacteria including hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9.

Viruses and bacteria target a variety of human cellular receptors. These cellular receptors include receptors that are part of the immunoglobulin superfamily, such as CD4, which is a co-receptor to the T-cell receptor, and can interact with MHC calls II molecules on the surface of the antigen presenting cell. CD4 is thought to be the primary receptor used by HIV-1 to gain entry into host T cells. Other receptors that are involved in entry of HIV-I are the chemokine receptors CCR5 and CXCR4.

Targets of the invention also include Toll-like receptors, such as hTLR4. Toll like receptors are a class of single membrane-spanning non-catalytic receptors that recognize structurally conserved molecules derived from viruses and bacteria.

Targets of the invention also include integrins such as human alphaV integrin, human beta3 integrin, human beta1 integrin and human alpha2 integrin. Integrin receptors are membrane receptors involved in cell adhesion and recognition in a variety of processes including embryogenesis, hemostasis, tissue repair, immune response and metatastatic diffusion of tumor cells. Integrins can act as cellular targets for viruses, such as HIV-1.

Targets of the invention also include members of the tetraspan family such as hCD81. The receptors mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility and are known to complex with integrins.

Targets of the invention also include scavenger receptors such as hSR-BI. hSR-BI facilitates high density lipoprotein cholesterol transport and correlates with protection against atherosclerosis.

Targets of the invention also include claudins, such as hClaudin-1, hClaudin-6 and hClaudin-9. Claudins are integral membrane proteins that are components of the tight junction strands and that may play a role in organ development.

Targets of the invention also include G protein coupled receptors (GPCRs) such as CXCR4 and CCR5. GPCRs are also known as seven transmembrane receptors, 7™ receptors, heptahelical receptors, and G protein linked receptors (GPLR), which are a protein family of transmembrane receptors that transduce an extracellular signal (ligand binding) into an intracellular signal (G protein activation). GPCRs are integral membrane proteins that possess seven membrane-spanning domains or transmembrane helices. The extracellular parts of the receptor can be glycosylated. These extracellular loops also contain two highly conserved cysteine residues which build disulfide bonds to stabilize the receptor structure. An overview of GPCRs can be found in standard handbooks, such as the G Protein Coupled Receptors Handbook, L. Devi (Ed.), Humana Press, 2005; as well as from the standard databases, such as GPCR DB (see for example http://www.gpcr.org/7tm/htmls/entries.html).

In the present description, examples and aspects:

-   a) Unless indicated or defined otherwise, all terms used have their     usual meaning in the art, which will be clear to the skilled person.     Reference is for example made to the standard handbooks, such as     Sambrook et al, “Molecular Cloning: A Laboratory Manual” (2nd.Ed.),     Vols. 1-3, Cold Spring Harbor Laboratory Press (1989); F. Ausubel et     al, eds., “Current protocols in molecular biology”, Green Publishing     and Wiley Interscience, New York (1987); Lewin, “Genes II”, John     Wiley & Sons, New York, N.Y., (1985); Old et al., “Principles of     Gene Manipulation: An Introduction to Genetic Engineering”, 2nd     edition, University of California Press, Berkeley, Calif. (1981);     Roitt et al., “Immunology” (6th. Ed.), Mosby/Elsevier, Edinburgh     (2001); Roitt et al., Roitt's Essential Immunology, 10^(th) Ed.     Blackwell Publishing, UK (2001); and Janeway et al., “Immunobiology”     (6th Ed.), Garland Science Publishing/Churchill Livingstone, New     York (2005), as well as to the general background art cited herein; -   b) Unless indicated otherwise, the term “immunoglobulin     sequence”—whether used herein to refer to a heavy chain antibody or     to a conventional 4-chain antibody—is used as a general term to     include both the full-size antibody, the individual chains thereof,     as well as all parts, domains or fragments thereof (including but     not limited to antigen-binding domains or fragments such as V_(HH)     domains or V_(H)/V_(L) domains, respectively). In addition, the term     “sequence” as used herein (for example in terms like “immunoglobulin     sequence”, “antibody sequence”, “variable domain sequence”, “V_(HH)     sequence” or “protein sequence”), should generally be understood to     include both the relevant amino acid sequence as well as nucleic     acids or nucleotide sequences encoding the same, unless the context     requires a more limited interpretation. Also, the term “nucleotide     sequence” as used herein also encompasses a nucleic acid molecule     with said nucleotide sequence, so that the terms “nucleotide     sequence” and “nucleic acid” should be considered equivalent and are     used interchangeably herein; -   c) Unless indicated otherwise, all methods, steps, techniques and     manipulations that are not specifically described in detail can be     performed and have been performed in a manner known per se, as will     be clear to the skilled person. Reference is for example again made     to the standard handbooks and the general background art mentioned     herein and to the further references cited therein; as well as to     for example the following reviews Presta, Adv. Drug Deliv. Rev.     2006, 58 (5-6): 640-56; Levin and Weiss, Mol. Biosyst. 2006, 2(1):     49-57; Irving et al., J. Immunol. Methods, 2001, 248(1-2), 31-45;     Schmitz et al., Placenta, 2000, 21 Suppl. A, S106-12, Gonzales et     al., Tumour Biol., 2005, 26(1), 31-43, which describe techniques for     protein engineering, such as affinity maturation and other     techniques for improving the specificity and other desired     properties of proteins such as immunoglobulins. -   d) Amino acid residues will be indicated according to the standard     three-letter or one-letter amino acid code, as mentioned in Table     A-2;

TABLE A-2 one-letter and three-letter ammo acid code Nonpolar, Alanine Ala A uncharged Valine Val V (at pH 6.0-7.0)⁽³⁾ Leucine Leu L Isoleucine Ile I Phenylalanine Phe F Methionine⁽¹⁾ Met M Tryptophan Trp W Proline Pro P Polar, Glycine⁽²⁾ Gly G uncharged Serine Ser S (at pH 6.0-7.0) Threonine Thr T Cysteine Cys C Asparagine Asn N Glutamine Gln Q Tyrosine Tyr Y Polar, Lysine Lys K charged Arginine Arg R (at pH 6.0-7.0) Histidine⁽⁴⁾ His H Aspartate Asp D Glutamate Glu E Notes: ⁽¹⁾Sometimes also considered to be a polar uncharged amino acid. ⁽²⁾Sometimes also considered to be a nonpolar uncharged amino acid. ⁽³⁾As will be clear to the skilled person, the fact that an amino acid residue is referred to in this Table as being either charged or uncharged at pH 6.0 to 7.0 does not reflect in any way on the charge said amino acid residue may have at a pH lower than 6.0 and/or at a pH higher than 7.0; the amino acid residues mentioned in the Table can be either charged and/or uncharged at such a higher or lower pH, as will be clear to the skilled person. ⁽⁴⁾As is known in the art, the charge of a His residue is greatly dependant upon even small shifts in pH, but a His residue can generally be considered essentially uncharged at a pH of about 6.5.

-   e) For the purposes of comparing two or more nucleotide sequences,     the percentage of “sequence identity” between a first nucleotide     sequence and a second nucleotide sequence may be calculated by     dividing [the number of nucleotides in the first nucleotide sequence     that are identical to the nucleotides at the corresponding positions     in the second nucleotide sequence] by [the total number of     nucleotides in the first nucleotide sequence] and multiplying by     [100%], in which each deletion, insertion, substitution or addition     of a nucleotide in the second nucleotide sequence—compared to the     first nucleotide sequence—is considered as a difference at a single     nucleotide (position).     -   Alternatively, the degree of sequence identity between two or         more nucleotide sequences may be calculated using a known         computer algorithm for sequence alignment such as NCBI Blast         v2.0, using standard settings.     -   Some other techniques, computer algorithms and settings for         determining the degree of sequence identity are for example         described in WO 04/037999, EP 0 967 284, EP 1 085 089, WO         00/55318, WO 00/78972, WO 98/49185 and GB 2 357 768-A.     -   Usually, for the purpose of determining the percentage of         “sequence identity” between two nucleotide sequences in         accordance with the calculation method outlined hereinabove, the         nucleotide sequence with the greatest number of nucleotides will         be taken as the “first” nucleotide sequence, and the other         nucleotide sequence will be taken as the “second” nucleotide         sequence; -   f) For the purposes of comparing two or more amino acid sequences,     the percentage of “sequence identity” between a first amino acid     sequence and a second amino acid sequence (also referred to herein     as “amino acid identity”) may be calculated by dividing [the number     of amino acid residues in the first amino acid sequence that are     identical to the amino acid residues at the corresponding positions     in the second amino acid sequence] by [the total number of amino     acid residues in the first amino acid sequence] and multiplying by     [100%], in which each deletion, insertion, substitution or addition     of an amino acid residue in the second amino acid sequence—compared     to the first amino acid sequence—is considered as a difference at a     single amino acid residue (position), i.e. as an “amino acid     difference” as defined herein.     -   Alternatively, the degree of sequence identity between two amino         acid sequences may be calculated using a known computer         algorithm, such as those mentioned above for determining the         degree of sequence identity for nucleotide sequences, again         using standard settings.     -   Usually, for the purpose of determining the percentage of         “sequence identity” between two amino acid sequences in         accordance with the calculation method outlined hereinabove, the         amino acid sequence with the greatest number of amino acid         residues will be taken as the “first” amino acid sequence, and         the other amino acid sequence will be taken as the “second”         amino acid sequence.     -   Also, in determining the degree of sequence identity between two         amino acid sequences, the skilled person may take into account         so-called “conservative” amino acid substitutions, which can         generally be described as amino acid substitutions in which an         amino acid residue is replaced with another amino acid residue         of similar chemical structure and which has little or         essentially no influence on the function, activity or other         biological properties of the polypeptide. Such conservative         amino acid substitutions are well known in the art, for example         from WO 04/037999, GB-A-3 357 768, WO 98/49185, WO 00/46383 and         WO 01/09300; and (preferred) types and/or combinations of such         substitutions may be selected on the basis of the pertinent         teachings from WO 04/037999 as well as WO 98/49185 and from the         further references cited therein.     -   Such conservative substitutions preferably are substitutions in         which one amino acid within the following groups (a)-(e) is         substituted by another amino acid residue within the same         group: (a) small aliphatic, nonpolar or slightly polar residues:         Ala, Ser, Thr, Pro and Gly; (b) polar, negatively charged         residues and their (uncharged) amides: Asp, Asn, Glu and         Gln; (c) polar, positively charged residues: His, Arg and         Lys; (d) large aliphatic, nonpolar residues: Met, Leu, Ile, Val         and Cys; and (e) aromatic residues: Phe, Tyr and Trp.     -   Particularly preferred conservative substitutions are as         follows: Ala into Gly or into Ser; Arg into Lys; Asn into Gln or         into His; Asp into Glu; Cys into Ser; Gln into Asn; Glu into         Asp; Gly into Ala or into Pro; His into Asn or into Gln; Ile         into Leu or into Val; Leu into Ile or into Val; Lys into Arg,         into Gln or into Glu; Met into Leu, into Tyr or into Ile; Phe         into Met, into Leu or into Tyr; Ser into Thr; Thr into Ser; Trp         into Tyr; Tyr into Trp; and/or Phe into Val, into Ile or into         Leu.     -   Any amino acid substitutions applied to the polypeptides         described herein may also be based on the analysis of the         frequencies of amino acid variations between homologous proteins         of different species developed by Schulz et al., Principles of         Protein Structure, Springer-Verlag, 1978, on the analyses of         structure forming potentials developed by Chou and Fasman,         Biochemistry 13: 211, 1974 and Adv. Enzymol., 47: 45-149, 1978,         and on the analysis of hydrophobicity patterns in proteins         developed by Eisenberg et al., Proc. Natl. Acad. Sci. USA 81:         140-144, 1984; Kyte & Doolittle; J. Molec. Biol. 157: 105-132,         198 1, and Goldman et al., Ann. Rev. Biophys. Chem. 15: 321-353,         1986, all incorporated herein in their entirety by reference.         Information on the primary, secondary and tertiary structure of         Nanobodies is given in the description herein and in the general         background art cited above. Also, for this purpose, the crystal         structure of a V_(HH) domain from a llama is for example given         by Desmyter et al., Nature Structural Biology, Vol. 3, 9, 803         (1996); Spinelli et al., Natural Structural Biology (1996); 3,         752-757; and Decanniere et al., Structure, Vol. 7, 4, 361         (1999). Further information about some of the amino acid         residues that in conventional V_(H) domains form the V_(H)/V_(L)         interface and potential camelizing substitutions on these         positions can be found in the prior art cited above. -   g) Amino acid sequences and nucleic acid sequences are said to be     “exactly the same” if they have 100% sequence identity (as defined     herein) over their entire length; -   h) When comparing two amino acid sequences, the term “amino acid     difference” refers to an insertion, deletion or substitution of a     single amino acid residue on a position of the first sequence,     compared to the second sequence; it being understood that two amino     acid sequences can contain one, two or more such amino acid     differences; -   i) When a nucleotide sequence or amino acid sequence is said to     “comprise” another nucleotide sequence or amino acid sequence,     respectively, or to “essentially consist of” another nucleotide     sequence or amino acid sequence, this may mean that the latter     nucleotide sequence or amino acid sequence has been incorporated     into the firstmentioned nucleotide sequence or amino acid sequence,     respectively, but more usually this generally means that the     firstmentioned nucleotide sequence or amino acid sequence comprises     within its sequence a stretch of nucleotides or amino acid residues,     respectively, that has the same nucleotide sequence or amino acid     sequence, respectively, as the latter sequence, irrespective of how     the firstmentioned sequence has actually been generated or obtained     (which may for example be by any suitable method described herein).     By means of a non-limiting example, when a Nanobody of the invention     is said to comprise a CDR sequence, this may mean that said CDR     sequence has been incorporated into the Nanobody of the invention,     but more usually this generally means that the Nanobody of the     invention contains within its sequence a stretch of amino acid     residues with the same amino acid sequence as said CDR sequence,     irrespective of how said Nanobody of the invention has been     generated or obtained. It should also be noted that when the latter     amino acid sequence has a specific biological or structural     function, it preferably has essentially the same, a similar or an     equivalent biological or structural function in the firstmentioned     amino acid sequence (in other words, the firstmentioned amino acid     sequence is preferably such that the latter sequence is capable of     performing essentially the same, a similar or an equivalent     biological or structural function). For example, when a Nanobody of     the invention is said to comprise a CDR sequence or framework     sequence, respectively, the CDR sequence and framework are     preferably capable, in said Nanobody, of functioning as a CDR     sequence or framework sequence, respectively. Also, when a     nucleotide sequence is said to comprise another nucleotide sequence,     the firstmentioned nucleotide sequence is preferably such that, when     it is expressed into an expression product (e.g. a polypeptide), the     amino acid sequence encoded by the latter nucleotide sequence forms     part of said expression product (in other words, that the latter     nucleotide sequence is in the same reading frame as the     firstmentioned, larger nucleotide sequence). -   j) A nucleic acid sequence or amino acid sequence is considered to     be “(in) essentially isolated (form)”—for example, compared to its     native biological source and/or the reaction medium or cultivation     medium from which it has been obtained—when it has been separated     from at least one other component with which it is usually     associated in said source or medium, such as another nucleic acid,     another protein/polypeptide, another biological component or     macromolecule or at least one contaminant, impurity or minor     component. In particular, a nucleic acid sequence or amino acid     sequence is considered “essentially isolated” when it has been     purified at least 2-fold, in particular at least 10-fold, more in     particular at least 100-fold, and up to 1000-fold or more. A nucleic     acid sequence or amino acid sequence that is “in essentially     isolated form” is preferably essentially homogeneous, as determined     using a suitable technique, such as a suitable chromatographical     technique, such as polyacrylamide-gel electrophoresis; -   k) The term “domain” as used herein generally refers to a globular     region of an amino acid sequence (such as an antibody chain, and in     particular to a globular region of a heavy chain antibody), or to a     polypeptide that essentially consists of such a globular region.     Usually, such a domain will comprise peptide loops (for example 3 or     4 peptide loops) stabilized, for example, as a sheet or by disulfide     bonds. The term “binding domain” refers to such a domain that is     directed against an antigenic determinant (as defined herein); -   l) The term “antigenic determinant” refers to the epitope on the     antigen recognized by the antigen-binding molecule (such as a     Nanobody or a polypeptide of the invention) and more in particular     by the antigen-binding site of said molecule. The terms “antigenic     determinant” and “epitope” may also be used interchangeably herein. -   m) An amino acid sequence (such as a Nanobody, an antibody, a     polypeptide of the invention, or generally an antigen binding     protein or polypeptide or a fragment thereof) that can     (specifically) bind to, that has affinity for and/or that has     specificity for a specific antigenic determinant, epitope, antigen     or protein (or for at least one part, fragment or epitope thereof)     is said to be “against” or “directed against” said antigenic     determinant, epitope, antigen or protein. -   n) The term “specificity” refers to the number of different types of     antigens or antigenic determinants to which a particular     antigen-binding molecule or antigen-binding protein (such as a     Nanobody or a polypeptide of the invention) molecule can bind. The     specificity of an antigen-binding protein can be determined based on     affinity and/or avidity. The affinity, represented by the     equilibrium constant for the dissociation of an antigen with an     antigen-binding protein (K_(D)), is a measure for the binding     strength between an antigenic determinant and an antigen-binding     site on the antigen-binding protein: the lesser the value of the     K_(D), the stronger the binding strength between an antigenic     determinant and the antigen-binding molecule (alternatively, the     affinity can also be expressed as the affinity constant (K_(A)),     which is 1/K_(D)). As will be clear to the skilled person (for     example on the basis of the further disclosure herein), affinity can     be determined in a manner known per se, depending on the specific     antigen of interest. Avidity is the measure of the strength of     binding between an antigen-binding molecule (such as a Nanobody or     polypeptide of the invention) and the pertinent antigen. Avidity is     related to both the affinity between an antigenic determinant and     its antigen binding site on the antigen-binding molecule and the     number of pertinent binding sites present on the antigen-binding     molecule. Typically, antigen-binding proteins (such as the amino     acid sequences, Nanobodies and/or polypeptides of the invention)     will bind to their antigen with a dissociation constant (K_(D)) of     10⁻⁵ to 10⁻¹² moles/liter or less, and preferably 10⁻⁷ to 10⁻¹²     moles/liter or less and more preferably 10⁻⁸ to 10⁻¹² moles/liter     (i.e. with an association constant (K_(A)) of 10⁵ to 10¹²     liter/moles or more, and preferably 10⁷ to 10¹² liter/moles or more     and more preferably 10⁸ to 10¹² liter/moles). Any K_(D) value     greater than 10⁴ mol/liter (or any K_(A) value lower than 10⁴ M⁻¹)     liters/mol is generally considered to indicate nonspecific binding.     Preferably, a monovalent immunoglobulin sequence of the invention     will bind to the desired antigen with an affinity less than 500 nM,     preferably less than 200 nM, more preferably less than 10 nM, such     as less than 500 pM. Specific binding of an antigen-binding protein     to an antigen or antigenic determinant can be determined in any     suitable manner known per se, including, for example, Scatchard     analysis and/or competitive binding assays, such as     radioimmunoassays (RIA), enzyme immunoassays (EIA) and sandwich     competition assays, and the different variants thereof known per se     in the art; as well as the other techniques mentioned herein.     -   The dissociation constant may be the actual or apparent         dissociation constant, as will be clear to the skilled person.         Methods for determining the dissociation constant will be clear         to the skilled person, and for example include the techniques         mentioned herein. In this respect, it will also be clear that it         may not be possible to measure dissociation constants of more         then 10⁻⁴ moles/liter or 10⁻³ moles/liter (e.g. of 10⁻²         moles/liter). Optionally, as will also be clear to the skilled         person, the (actual or apparent) dissociation constant may be         calculated on the basis of the (actual or apparent) association         constant (K_(A)), by means of the relationship [K_(D)=1/K_(A)].     -   The affinity denotes the strength or stability of a molecular         interaction. The affinity is commonly given as by the K_(D), or         dissociation constant, which has units of mol/liter (or M). The         affinity can also be expressed as an association constant,         K_(A), which equals 1/K_(D) and has units of (mol/liter)⁻¹ (or         M⁻¹). In the present specification, the stability of the         interaction between two molecules (such as an amino acid         sequence, Nanobody or polypeptide of the invention and its         intended target) will mainly be expressed in terms of the K_(D)         value of their interaction; it being clear to the skilled person         that in view of the relation K_(A)=1/K_(D), specifying the         strength of molecular interaction by its K_(D) value can also be         used to calculate the corresponding K_(A) value. The K_(D)-value         characterizes the strength of a molecular interaction also in a         thermodynamic sense as it is related to the free energy (DG) of         binding by the well known relation DG=RT.ln(K_(D)) (equivalently         DG=−RT.ln(K_(A))), where R equals the gas constant, T equals the         absolute temperature and ln denotes the natural logarithm.     -   The K_(D) for biological interactions which are considered         meaningful (e.g. specific) are typically in the range of 10⁻¹⁰ M         (0.1 nM) to 10⁻⁵M (10000 nM). The stronger an interaction is,         the lower is its K_(D).     -   The K_(D) can also be expressed as the ratio of the dissociation         rate constant of a complex, denoted as k_(off), to the rate of         its association, denoted k_(on) (so that K_(D)=k_(off)/k_(on)         and K_(A)=k_(on)/k_(off)). The off-rate k_(off) has units s⁻¹         (where s is the SI unit notation of second). The on-rate k_(on)         has units M⁻¹s⁻¹. The on-rate may vary between 10² M⁻¹s⁻¹ to         about 10⁷ M⁻¹s⁻¹, approaching the diffusion-limited association         rate constant for bimolecular interactions. The off-rate is         related to the half-life of a given molecular interaction by the         relation t_(1/2)=ln(2)/k_(off). The off-rate may vary between         10⁻⁶ s⁻¹ (near irreversible complex with a t_(1/2) of multiple         days) to 1 s⁻¹ (t_(1/2)=0.69 s).     -   The affinity of a molecular interaction between two molecules         can be measured via different techniques known per se, such as         the well known surface plasmon resonance (SPR) biosensor         technique (see for example Ober et al., Intern. Immunology, 13,         1551-1559, 2001) where one molecule is immobilized on the         biosensor chip and the other molecule is passed over the         immobilized molecule under flow conditions yielding k_(on),         k_(off) measurements and hence K_(D) (or K_(A)) values. This can         for example be performed using the well-known BIACORE         instruments.     -   It will also be clear to the skilled person that the measured         K_(D) may correspond to the apparent K_(D) if the measuring         process somehow influences the intrinsic binding affinity of the         implied molecules for example by artefacts related to the         coating on the biosensor of one molecule. Also, an apparent         K_(D) may be measured if one molecule contains more than one         recognition sites for the other molecule. In such situation the         measured affinity may be affected by the avidity of the         interaction by the two molecules.     -   Another approach that may be used to assess affinity is the         2-step ELISA (Enzyme-Linked Immunosorbent Assay) procedure of         Friguet et al. (J. Immunol. Methods, 77, 305-19, 1985). This         method establishes a solution phase binding equilibrium         measurement and avoids possible artefacts relating to adsorption         of one of the molecules on a support such as plastic.     -   However, the accurate measurement of K_(D) may be quite         labor-intensive and as consequence, often apparent K_(D) values         are determined to assess the binding strength of two molecules.         It should be noted that as long all measurements are made in a         consistent way (e.g. keeping the assay conditions unchanged)         apparent K_(D) measurements can be used as an approximation of         the true K_(D) and hence in the present document K_(D) and         apparent K_(D) should be treated with equal importance or         relevance. Finally, it should be noted that in many situations         the experienced scientist may judge it to be convenient to         determine the binding affinity relative to some reference         molecule. For example, to assess the binding strength between         molecules A and B, one may e.g. use a reference molecule C that         is known to bind to B and that is suitably labelled with a         fluorophore or chromophore group or other chemical moiety, such         as biotin for easy detection in an ELISA or FACS (Fluorescent         activated cell sorting) or other format (the fluorophore for         fluorescence detection, the chromophore for light absorption         detection, the biotin for streptavidin-mediated ELISA         detection). Typically, the reference molecule C is kept at a         fixed concentration and the concentration of A is varied for a         given concentration or amount of B. As a result an IC₅₀ value is         obtained corresponding to the concentration of A at which the         signal measured for C in absence of A is halved. Provided         K_(D ref), the K_(D) of the reference molecule, is known, as         well as the total concentration c_(ref) of the reference         molecule, the apparent K_(D) for the interaction A-B can be         obtained from following formula:         K_(D)=IC₅₀/(1+c_(ref)/K_(D ref)). Note that if         c_(ref)<<K_(D ref), K_(D)≈IC₅₀. Provided the measurement of the         IC₅₀ is performed in a consistent way (e.g. keeping c_(ref)         fixed) for the binders that are compared, the strength or         stability of a molecular interaction can be assessed by the IC₅₀         and this measurement is judged as equivalent to K_(D) or to         apparent K_(D) throughout this text. -   o) The half-life of an amino acid sequence, compound or polypeptide     of the invention can generally be defined as the time taken for the     serum concentration of the amino acid sequence, compound or     polypeptide to be reduced by 50%, in vivo, for example due to     degradation of the sequence or compound and/or clearance or     sequestration of the sequence or compound by natural mechanisms. The     in vivo half-life of an amino acid sequence, compound or polypeptide     of the invention can be determined in any manner known per se, such     as by pharmacokinetic analysis. Suitable techniques will be clear to     the person skilled in the art, and may for example generally involve     the steps of suitably administering to a warm-blooded animal (i.e.     to a human or to another suitable mammal, such as a mouse, rabbit,     rat, pig, dog or a primate, for example monkeys from the genus     Macaca (such as, and in particular, cynomolgus monkeys (Macaca     fascicularis) and/or rhesus monkeys (Macaca mulatta)) and baboon     (Papio ursinus)) a suitable dose of the amino acid sequence,     compound or polypeptide of the invention; collecting blood samples     or other samples from said animal; determining the level or     concentration of the amino acid sequence, compound or polypeptide of     the invention in said blood sample; and calculating, from (a plot     of) the data thus obtained, the time until the level or     concentration of the amino acid sequence, compound or polypeptide of     the invention has been reduced by 50% compared to the initial level     upon dosing. Reference is for example made to the Experimental Part     below, as well as to the standard handbooks, such as Kenneth, A et     al: Chemical Stability of Pharmaceuticals: A Handbook for     Pharmacists and Peters et al, Pharmacokinete analysis: A Practical     Approach (1996). Reference is also made to “Pharmacokinetics”, M     Gibaldi & D Perron, published by Marcel Dekker, 2nd Rev. edition     (1982).     -   As will also be clear to the skilled person (see for example         pages 6 and 7 of WO 04/003019 and in the further references         cited therein), the half-life can be expressed using parameters         such as the t1/2-alpha, t1/2-beta and the area under the curve         (AUC). In the present specification, an “increase in half-life”         refers to an increase in any one of these parameters, such as         any two of these parameters, or essentially all three these         parameters. As used herein “increase in half-life” or “increased         half-life” in particular refers to an increase in the t1/2-beta,         either with or without an increase in the t1/2-alpha and/or the         AUC or both. -   p) In the context of the present invention, “modulating” or “to     modulate” generally means either reducing or inhibiting the activity     of, or alternatively increasing the activity of a target or antigen,     as measured using a suitable in vitro, cellular or in vivo assay. In     particular, “modulating” or “to modulate” may mean either reducing     or inhibiting the activity of, or alternatively increasing a     (relevant or intended) biological activity of, a target or antigen,     as measured using a suitable in vitro, cellular or in vivo assay     (which will usually depend on the target or antigen involved), by at     least 1%, preferably at least 5%, such as at least 10% or at least     25%, for example by at least 50%, at least 60%, at least 70%, at     least 80%, or 90% or more, compared to activity of the target or     antigen in the same assay under the same conditions but without the     presence of the construct of the invention.     -   As will be clear to the skilled person, “modulating” may also         involve effecting a change (which may either be an increase or a         decrease) in affinity, avidity, specificity and/or selectivity         of a target or antigen for one or more of its ligands, binding         partners, partners for association into a homomultimeric or         heteromultimeric form, or substrates; and/or effecting a change         (which may either be an increase or a decrease) in the         sensitivity of the target or antigen for one or more conditions         in the medium or surroundings in which the target or antigen is         present (such as pH, ion strength, the presence of co-factors,         etc.), compared to the same conditions but without the presence         of the construct of the invention. As will be clear to the         skilled person, this may again be determined in any suitable         manner and/or using any suitable assay known per se, depending         on the target or antigen involved.     -   “Modulating” may also mean effecting a change (i.e. an activity         as an agonist, as an antagonist or as a reverse agonist,         respectively, depending on the target or antigen and the desired         biological or physiological effect) with respect to one or more         biological or physiological mechanisms, effects, responses,         functions, pathways or activities in which the target or antigen         (or in which its substrate(s), ligand(s) or pathway(s) are         involved, such as its signalling pathway or metabolic pathway         and their associated biological or physiological effects) is         involved. Again, as will be clear to the skilled person, such an         action as an agonist or an antagonist may be determined in any         suitable manner and/or using any suitable (in vitro and usually         cellular or in assay) assay known per se, depending on the         target or antigen involved. In particular, an action as an         agonist or antagonist may be such that an intended biological or         physiological activity is increased or decreased, respectively,         by at least 1%, preferably at least 5%, such as at least 10% or         at least 25%, for example by at least 50%, at least 60%, at         least 70%, at least 80%, or 90% or more, compared to the         biological or physiological activity in the same assay under the         same conditions but without the presence of the construct of the         invention.     -   Modulating may for example also involve allosteric modulation of         the target or antigen; and/or reducing or inhibiting the binding         of the target or antigen to one of its substrates or ligands         and/or competing with a natural ligand, substrate for binding to         the target or antigen. Modulating may also involve activating         the target or antigen or the mechanism or pathway in which it is         involved. Modulating may for example also involve effecting a         change in respect of the folding or confirmation of the target         or antigen, or in respect of the ability of the target or         antigen to fold, to change its confirmation (for example, upon         binding of a ligand), to associate with other (sub)units, or to         disassociate.     -   Modulating may for example also involve effecting a change in         the ability of the target or antigen to transport other         compounds or to serve as a channel for other compounds (such as         ions).     -   Modulating may be reversible or irreversible, but for         pharmaceutical and pharmacological purposes will usually be in a         reversible manner. -   q) In respect of a target or antigen, the term “interaction site” on     the target or antigen means a site, epitope, antigenic determinant,     part, domain or stretch of amino acid residues on the target or     antigen that is a site for binding to a ligand, receptor or other     binding partner, a catalytic site, a cleavage site, a site for     allosteric interaction, a site involved in multimerisation (such as     homomerization or heterodimerization) of the target or antigen; or     any other site, epitope, antigenic determinant, part, domain or     stretch of amino acid residues on the target or antigen that is     involved in a biological action or mechanism of the target or     antigen. More generally, an “interaction site” can be any site,     epitope, antigenic determinant, part, domain or stretch of amino     acid residues on the target or antigen to which an amino acid     sequence or polypeptide of the invention can bind such that the     target or antigen (and/or any pathway, interaction, signalling,     biological mechanism or biological effect in which the target or     antigen is involved) is modulated (as defined herein). -   r) An amino acid sequence or polypeptide is said to be “specific     for” a first target or antigen compared to a second target or     antigen when is binds to the first antigen with an affinity (as     described above, and suitably expressed as a K_(D) value, K_(A)     value, K_(off) rate and/or K_(on) rate) that is at least 10 times,     such as at least 100 times, and preferably at least 1000 times, and     up to 10.000 times or more better than the affinity with which said     amino acid sequence or polypeptide binds to the second target or     polypeptide. For example, the first antigen may bind to the target     or antigen with a K_(D) value that is at least 10 times less, such     as at least 100 times less, and preferably at least 1000 times less,     such as 10.000 times less or even less than that, than the K_(D)     with which said amino acid sequence or polypeptide binds to the     second target or polypeptide. Preferably, when an amino acid     sequence or polypeptide is “specific for” a first target or antigen     compared to a second target or antigen, it is directed against (as     defined herein) said first target or antigen, but not directed     against said second target or antigen. -   s) The terms “cross-block”, “cross-blocked” and “cross-blocking” are     used interchangeably herein to mean the ability of an amino acid     sequence or other binding agents (such as a Nanobody, polypeptide or     compound or construct of the invention) to interfere with the     binding of other amino acid sequences or binding agents of the     invention to a given target. The extend to which an amino acid     sequence or other binding agents of the invention is able to     interfere with the binding of another to [target], and therefore     whether it can be said to cross-block according to the invention,     can be determined using competition binding assays. One particularly     suitable quantitative cross-blocking assay uses a Biacore machine     which can measure the extent of interactions using surface plasmon     resonance technology. Another suitable quantitative cross-blocking     assay uses an ELISA-based approach to measure competition between     amino acid sequences or other binding agents in terms of their     binding to the target.     -   The following generally describes a suitable Biacore assay for         determining whether an amino acid sequence or other binding         agent cross-blocks or is capable of cross-blocking according to         the invention. It will be appreciated that the assay can be used         with any of the amino acid sequences or other binding agents         described herein. The Biacore machine (for example the         Biacore 3000) is operated in line with the manufacturer's         recommendations. Thus in one cross-blocking assay, the target         protein is coupled to a CM5 Biacore chip using standard amine         coupling chemistry to generate a surface that is coated with the         target. Typically 200-800 resonance units of the target would be         coupled to the chip (an amount that gives easily measurable         levels of binding but that is readily saturable by the         concentrations of test reagent being used). Two test amino acid         sequences (termed A* and B*) to be assessed for their ability to         cross-block each other are mixed at a one to one molar ratio of         binding sites in a suitable buffer to create the test mixture.         When calculating the concentrations on a binding site basis the         molecular weight of an amino acid sequence is assumed to be the         total molecular weight of the amino acid sequence divided by the         number of target binding sites on that amino acid sequence. The         concentration of each amino acid sequence in the test mix should         be high enough to readily saturate the binding sites for that         amino acid sequence on the target molecules captured on the         Biacore chip. The amino acid sequences in the mixture are at the         same molar concentration (on a binding basis) and that         concentration would typically be between 1.00 and 1.5 micromolar         (on a binding site basis). Separate solutions containing A*         alone and B* alone are also prepared. A* and B* in these         solutions should be in the same buffer and at the same         concentration as in the test mix. The test mixture is passed         over the target-coated Biacore chip and the total amount of         binding recorded. The chip is then treated in such a way as to         remove the bound amino acid sequences without damaging the         chip-bound target. Typically this is done by treating the chip         with 30 mM HCl for 60 seconds. The solution of A* alone is then         passed over the target-coated surface and the amount of binding         recorded. The chip is again treated to remove all of the bound         amino acid sequences without damaging the chip-bound target. The         solution of B* alone is then passed over the target-coated         surface and the amount of binding recorded. The maximum         theoretical binding of the mixture of A* and B* is next         calculated, and is the sum of the binding of each amino acid         sequence when passed over the target surface alone. If the         actual recorded binding of the mixture is less than this         theoretical maximum then the two amino acid sequences are         cross-blocking each other. Thus, in general, a cross-blocking         amino acid sequence or other binding agent according to the         invention is one which will bind to the target in the above         Biacore cross-blocking assay such that, during the assay and in         the presence of a second amino acid sequence or other binding         agent of the invention, the recorded binding is between 80% and         0.1% (e.g. 80% to 4%) of the maximum theoretical binding,         specifically between 75% and 0.1% (e.g. 75% to 4%) of the         maximum theoretical binding, and more specifically between 70%         and 0.1% (e.g. 70% to 4%) of maximum theoretical binding (as         just defined above) of the two amino acid sequences or binding         agents in combination. The Biacore assay described above is a         primary assay used to determine if amino acid sequences or other         binding agents cross-block each other according to the         invention. On rare occasions particular amino acid sequences or         other binding agents may not bind to target coupled via amine         chemistry to a CM5 Biacore chip (this usually occurs when the         relevant binding site on target is masked or destroyed by the         coupling to the chip). In such cases cross-blocking can be         determined using a tagged version of the target, for example a         N-terminal His-tagged version. In this particular format, an         anti-His amino acid sequence would be coupled to the Biacore         chip and then the His-tagged target would be passed over the         surface of the chip and captured by the anti-His amino acid         sequence. The cross blocking analysis would be carried out         essentially as described above, except that after each chip         regeneration cycle, new His-tagged target would be loaded back         onto the anti-His amino acid sequence coated surface. In         addition to the example given using N-terminal His-tagged         target, C-terminal His-tagged target could alternatively be         used. Furthermore, various other tags and tag binding protein         combinations that are known in the art could be used for such a         cross-blocking analysis (e.g. HA tag with anti-HA antibodies;         FLAG tag with anti-FLAG antibodies; biotin tag with         streptavidin).     -   The following generally describes an ELISA assay for determining         whether an amino acid sequence or other binding agent directed         against a target cross-blocks or is capable of cross-blocking as         defined herein. It will be appreciated that the assay can be         used with any of the amino acid sequences (or other binding         agents such as polypeptides of the invention) described herein.         The general principal of the assay is to have an amino acid         sequence or binding agent that is directed against the target         coated onto the wells of an ELISA plate. An excess amount of a         second, potentially cross-blocking, anti-target amino acid         sequence is added in solution (i.e. not bound to the ELISA         plate). A limited amount of the target is then added to the         wells. The coated amino acid sequence and the amino acid         sequence in solution compete for binding of the limited number         of target molecules. The plate is washed to remove excess target         that has not been bound by the coated amino acid sequence and to         also remove the second, solution phase amino acid sequence as         well as any complexes formed between the second, solution phase         amino acid sequence and target. The amount of bound target is         then measured using a reagent that is appropriate to detect the         target. An amino acid sequence in solution that is able to         cross-block the coated amino acid sequence will be able to cause         a decrease in the number of target molecules that the coated         amino acid sequence can bind relative to the number of target         molecules that the coated amino acid sequence can bind in the         absence of the second, solution phase, amino acid sequence. In         the instance where the first amino acid sequence, e.g. an Ab-X,         is chosen to be the immobilized amino acid sequence, it is         coated onto the wells of the ELISA plate, after which the plates         are blocked with a suitable blocking solution to minimize         non-specific binding of reagents that are subsequently added. An         excess amount of the second amino acid sequence, i.e. Ab-Y, is         then added to the ELISA plate such that the moles of Ab-Y target         binding sites per well are at least 10 fold higher than the         moles of Ab-X target binding sites that were used, per well,         during the coating of the ELISA plate. Target is then added such         that the moles of target added per well are at least 25-fold         lower than the moles of Ab-X target binding sites that were used         for coating each well. Following a suitable incubation period         the ELISA plate is washed and a reagent for detecting the target         is added to measure the amount of target specifically bound by         the coated anti-target amino acid sequence (in this case Ab-X).         The background signal for the assay is defined as the signal         obtained in wells with the coated amino acid sequence (in this         case Ab-X), second solution phase amino acid sequence (in this         case Ab-Y), target buffer only (i.e. without target) and target         detection reagents. The positive control signal for the assay is         defined as the signal obtained in wells with the coated amino         acid sequence (in this case Ab-X), second solution phase amino         acid sequence buffer only (i.e. without second solution phase         amino acid sequence), target and target detection reagents. The         ELISA assay may be run in such a manner so as to have the         positive control signal be at least 6 times the background         signal. To avoid any artefacts (e.g. significantly different         affinities between Ab-X and Ab-Y for the target) resulting from         the choice of which amino acid sequence to use as the coating         amino acid sequence and which to use as the second (competitor)         amino acid sequence, the cross-blocking assay may to be run in         two formats: 1) format 1 is where Ab-X is the amino acid         sequence that is coated onto the ELISA plate and Ab-Y is the         competitor amino acid sequence that is in solution and 2) format         2 is where Ab-Y is the amino acid sequence that is coated onto         the ELISA plate and Ab-X is the competitor amino acid sequence         that is in solution. Ab-X and Ab-Y are defined as cross-blocking         if, either in format 1 or in format 2, the solution phase         anti-target amino acid sequence is able to cause a reduction of         between 60% and 100%, specifically between 70% and 100%, and         more specifically between 80% and 100%, of the target detection         signal (i.e. the amount of target bound by the coated amino acid         sequence) as compared to the target detection signal obtained in         the absence of the solution phase anti-target amino acid         sequence (i.e. the positive control wells). -   t) An amino acid sequence is said to be “cross-reactive” for two     different antigens or antigenic determinants (such as serum albumin     from two different species of mammal, such as human serum albumin     and cyno serum albumin) if it is specific for (as defined herein)     both these different antigens or antigenic determinants. -   u) By binding that is “essentially independent of the pH” is     generally meant herein that the association constant (K_(A)) of the     amino acid sequence with respect to the serum protein (such as serum     albumin) at the pH value(s) that occur in a cell of an animal or     human body (as further described herein) is at least 5%, such as at     least 10%, preferably at least 25%, more preferably at least 50%,     even more preferably at least 60%, such as even more preferably at     least 70%, such as at least 80% or 90% or more (or even more than     100%, such as more than 110%, more than 120% or even 130% or more,     or even more than 150%, or even more than 200%) of the association     constant (K_(A)) of the amino acid sequence with respect to the same     serum protein at the pH value(s) that occur outside said cell.     Alternatively, by binding that is “essentially independent of the     pH” is generally meant herein that the k_(off) rate (measured by     Biacore) of the amino acid sequence with respect to the serum     protein (such as serum albumin) at the pH value(s) that occur in a     cell of an animal or human body (as e.g. further described herein,     e.g. pH around 5.5, e.g. 5.3 to 5.7) is at least 5%, such as at     least 10%, preferably at least 25%, more preferably at least 50%,     even more preferably at least 60%, such as even more preferably at     least 70%, such as at least 80% or 90% or more (or even more than     100%, such as more than 110%, more than 120% or even 130% or more,     or even more than 150%, or even more than 200%) of the k_(off)-rate     of the amino acid sequence with respect to the same serum protein at     the pH value(s) that occur outside said cell, e.g. pH 7.2 to 7.4. By     “the pH value(s) that occur in a cell of an animal or human body” is     meant the pH value(s) that may occur inside a cell, and in     particular inside a cell that is involved in the recycling of the     serum protein. In particular, by “the pH value(s) that occur in a     cell of an animal or human body” is meant the pH value(s) that may     occur inside a (sub)cellular compartment or vesicle that is involved     in recycling of the serum protein (e.g. as a result of pinocytosis,     endocytosis, transcytosis, exocytosis and phagocytosis or a similar     mechanism of uptake or internalization into said cell), such as an     endosome, lysosome or pinosome. -   v) As further described herein, the total number of amino acid     residues in a Nanobody can be in the region of 110-120, is     preferably 112-115, and is most preferably 113. It should however be     noted that parts, fragments, analogs or derivatives (as further     described herein) of a Nanobody are not particularly limited as to     their length and/or size, as long as such parts, fragments, analogs     or derivatives meet the further requirements outlined herein and are     also preferably suitable for the purposes described herein; -   w) The amino acid residues of a Nanobody are numbered according to     the general numbering for V_(H) domains given by Kabat et al.     (“Sequence of proteins of immunological interest”, US Public Health     Services, NIH Bethesda, Md., Publication No. 91), as applied to     V_(HH) domains from Camelids in the article of Riechmann and     Muyldermans, J. Immunol. Methods 2000 Jun. 23; 240 (1-2): 185-195;     or referred to herein. According to this numbering, FR1 of a     Nanobody comprises the amino acid residues at positions 1-30, CDR1     of a Nanobody comprises the amino acid residues at positions 31-35,     FR2 of a Nanobody comprises the amino acids at positions 36-49, CDR2     of a Nanobody comprises the amino acid residues at positions 50-65.     FR3 of a Nanobody comprises the amino acid residues at positions     66-94, CDR3 of a Nanobody comprises the amino acid residues at     positions 95-102, and FR4 of a Nanobody comprises the amino acid     residues at positions 103-113. [In this respect, it should be noted     that—as is well known in the art for V_(H) domains and for V_(HH)     domains—the total number of amino acid residues in each of the CDR's     may vary and may not correspond to the total number of amino acid     residues indicated by the Kabat numbering (that is, one or more     positions according to the Kabat numbering may not be occupied in     the actual sequence, or the actual sequence may contain more amino     acid residues than the number allowed for by the Kabat numbering).     This means that, generally, the numbering according to Kabat may or     may not correspond to the actual numbering of the amino acid     residues in the actual sequence. Generally, however, it can be said     that, according to the numbering of Kabat and irrespective of the     number of amino acid residues in the CDR's, position 1 according to     the Kabat numbering corresponds to the start of FR1 and vice versa,     position 36 according to the Kabat numbering corresponds to the     start of FR2 and vice versa, position 66 according to the Kabat     numbering corresponds to the start of FR3 and vice versa, and     position 103 according to the Kabat numbering corresponds to the     start of FR4 and vice versa.].     -   Alternative methods for numbering the amino acid residues of         V_(H) domains, which methods can also be applied in an analogous         manner to V_(HH) domains from Camelids and to Nanobodies, are         the method described by Chothia et al. (Nature 342, 877-883         (1989)), the so-called “AbM definition” and the so-called         “contact definition”. However, in the present description,         aspects and figures, the numbering according to Kabat as applied         to V_(HH) domains by Riechmann and Muyldermans will be followed,         unless indicated otherwise; and -   x) The Figures, Sequence Listing and the Experimental Part/Examples     are only given to further illustrate the invention and should not be     interpreted or construed as limiting the scope of the invention     and/or of the appended aspects in any way, unless explicitly     indicated otherwise herein.

For a general description of heavy chain antibodies and the variable domains thereof, reference is inter alia made to the prior art cited herein, to the review article by Muyldermans in Reviews in Molecular Biotechnology 74(2001), 277-302; as well as to the following patent applications, which are mentioned as general background art: WO 94/04678, WO 95/04079 and WO 96/34103 of the Vrije Universiteit Brussel; WO 94/25591, WO 99/37681, WO 00/40968, WO 00/43507, WO 00/65057, WO 01/40310, WO 01/44301, EP 1134231 and WO 02/48193 of Unilever; WO 97/49805, WO 01/21817, WO 03/035694, WO 03/054016 and WO 03/055527 of the Vlaams Instituut voor Biotechnologie (VIB); WO 03/050531 of Algonomics N.V. and Ablynx N.V.; WO 01/90190 by the National Research Council of Canada; WO 03/025020 (=EP 1 433 793) by the Institute of Antibodies; as well as WO 04/041867, WO 04/041862, WO 04/041865, WO 04/041863, WO 04/062551, WO 05/044858, WO 06/40153, WO 06/079372, WO 06/122786, WO 06/122787 and WO 06/122825, by Ablynx N.V. and the further published patent applications by Ablynx N.V. Reference is also made to the further prior art mentioned in these applications, and in particular to the list of references mentioned on pages 41-43 of the International application WO 06/040153, which list and references are incorporated herein by reference.

In accordance with the terminology used in the art (see the above references), the variable domains present in naturally occurring heavy chain antibodies will also be referred to as “V_(HH) domains”, in order to distinguish them from the heavy chain variable domains that are present in conventional 4-chain antibodies (which will be referred to hereinbelow as “V_(H) domains”) and from the light chain variable domains that are present in conventional 4-chain antibodies (which will be referred to hereinbelow as “V_(L) domains”).

As mentioned in the prior art referred to above, V_(HH) domains have a number of unique structural characteristics and functional properties which make isolated V_(HH) domains (as well as Nanobodies based thereon, which share these structural characteristics and functional properties with the naturally occurring V_(HH) domains) and proteins containing the same highly advantageous for use as functional antigen-binding domains or proteins. In particular, and without being limited thereto, V_(HH) domains (which have been “designed” by nature to functionally bind to an antigen without the presence of, and without any interaction with, a light chain variable domain) and Nanobodies can function as a single, relatively small, functional antigen-binding structural unit, domain or protein. This distinguishes the V_(HH) domains from the V_(H) and V_(L) domains of conventional 4-chain antibodies, which by themselves are generally not suited for practical application as single antigen-binding proteins or domains, but need to be combined in some form or another to provide a functional antigen-binding unit (as in for example conventional antibody fragments such as Fab fragments; in ScFv's fragments, which consist of a V_(H) domain covalently linked to a V_(L) domain).

Because of these unique properties, the use of V_(HH) domains and Nanobodies as single antigen-binding proteins or as antigen-binding domains (i.e. as part of a larger protein or polypeptide) offers a number of significant advantages over the use of conventional V_(H) and V_(L) domains, scFv's or conventional antibody fragments (such as Fab- or F(ab′)₂-fragments):

-   -   only a single domain is required to bind an antigen with high         affinity and with high selectivity, so that there is no need to         have two separate domains present, nor to assure that these two         domains are present in the right spatial conformation and         configuration (i.e. through the use of especially designed         linkers, as with scFv's);     -   V_(HH) domains and Nanobodies can be expressed from a single         gene and require no post-translational folding or modifications;     -   V_(HH) domains and Nanobodies can easily be engineered into         multivalent and multispecific formats (as further discussed         herein);     -   V_(HH) domains and Nanobodies are highly soluble and do not have         a tendency to aggregate (as with the mouse-derived “dAb's”         described by Ward et al., Nature, Vol. 341, 1989, p. 544);     -   V_(HH) domains and Nanobodies are highly stable to heat, pH,         proteases and other denaturing agents or conditions (see for         example Ewert et al, supra);     -   V_(HH) domains and Nanobodies are easy and relatively cheap to         prepare, even on a scale required for production. For example,         V_(HH) domains, Nanobodies and proteins/polypeptides containing         the same can be produced using microbial fermentation (e.g. as         further described below) and do not require the use of mammalian         expression systems, as with for example conventional antibody         fragments;     -   V_(HH) domains and Nanobodies are relatively small         (approximately 15 kDa, or 10 times smaller than a conventional         IgG) compared to conventional 4-chain antibodies and         antigen-binding fragments thereof, and therefore show high(er)         penetration into tissues (including but not limited to solid         tumors and other dense tissues) than such conventional 4-chain         antibodies and antigen-binding fragments thereof;     -   V_(HH) domains and Nanobodies can show so-called cavity-binding         properties (inter alia due to their extended CDR3 loop, compared         to conventional V_(H) domains) and can therefore also access         targets and epitopes not accessible to conventional 4-chain         antibodies and antigen-binding fragments thereof. For example,         it has been shown that V_(HH) domains and Nanobodies can inhibit         enzymes (see for example WO 97/49805; Transue et al., Proteins         1998 Sep. 1; 32(4): 515-22; Lauwereys et al., EMBO J. 1998 Jul.         1; 17(13): 3512-20).

In a specific and preferred aspect, the invention provides Nanobodies against Targets of the invention, and in particular Nanobodies against Targets of the invention from a warm-blooded animal, and more in particular Nanobodies against Targets of the invention from a mammal, and especially Nanobodies against human Targets of the invention; as well as proteins and/or polypeptides comprising at least one such Nanobody.

In particular, the invention provides Nanobodies against Targets of the invention, and proteins and/or polypeptides comprising the same, that have improved therapeutic and/or pharmacological properties and/or other advantageous properties (such as, for example, improved ease of preparation and/or reduced costs of goods), compared to conventional antibodies against Targets of the invention or fragments thereof, compared to constructs that could be based on such conventional antibodies or antibody fragments (such as Fab′ fragments, F(ab′)₂ fragments, ScFv constructs, “diabodies” and other multispecific constructs (see for example the review by Holliger and Hudson, Nat Biotechnol. 2005 September; 23(9):1126-36)), and also compared to the so-called “dAb's” or similar (single) domain antibodies that may be derived from variable domains of conventional antibodies. These improved and advantageous properties will become clear from the further description herein, and for example include, without limitation, one or more of:

-   -   increased affinity and/or avidity for Targets of the invention,         either in a monovalent format, in a multivalent format (for         example in a bivalent format) and/or in a multispecific format         (for example one of the multispecific formats described         hereinbelow);     -   better suitability for formatting in a multivalent format (for         example in a bivalent format);     -   better suitability for formatting in a multispecific format (for         example one of the multispecific formats described hereinbelow);     -   improved suitability or susceptibility for “humanizing”         substitutions (as defined herein);     -   less immunogenicity, either in a monovalent format, in a         multivalent format (for example in a bivalent format) and/or in         a multispecific format (for example one of the multispecific         formats described hereinbelow);     -   increased stability, either in a monovalent format, in a         multivalent format (for example in a bivalent format) and/or in         a multispecific format (for example one of the multispecific         formats described hereinbelow);     -   increased specificity towards Targets of the invention, either         in a monovalent format, in a multivalent format (for example in         a bivalent format) and/or in a multispecific format (for example         one of the multispecific formats described hereinbelow);     -   decreased or where desired increased cross-reactivity with         Targets of the invention from different species;         and/or     -   one or more other improved properties desirable for         pharmaceutical use (including prophylactic use and/or         therapeutic use) and/or for diagnostic use (including but not         limited to use for imaging purposes), either in a monovalent         format, in a multivalent format (for example in a bivalent         format) and/or in a multispecific format (for example one of the         multispecific formats described hereinbelow).

As generally described herein for the amino acid sequences of the invention, the Nanobodies of the invention are preferably in essentially isolated form (as defined herein), or form part of a protein or polypeptide of the invention (as defined herein), which may comprise or essentially consist of one or more Nanobodies of the invention and which may optionally further comprise one or more further amino acid sequences (all optionally linked via one or more suitable linkers). For example, and without limitation, the one or more amino acid sequences of the invention may be used as a binding unit in such a protein or polypeptide, which may optionally contain one or more further amino acid sequences that can serve as a binding unit (i.e. against one or more other targets than Targets of the invention), so as to provide a monovalent, multivalent or multispecific polypeptide of the invention, respectively, all as described herein. In particular, such a protein or polypeptide may comprise or essentially consist of one or more Nanobodies of the invention and optionally one or more (other) Nanobodies (i.e. directed against other targets than Targets of the invention), all optionally linked via one or more suitable linkers, so as to provide a monovalent, multivalent or multispecific Nanobody construct, respectively, as further described herein. Such proteins or polypeptides may also be in essentially isolated form (as defined herein).

In a Nanobody of the invention, the binding site for binding against Targets of the invention is preferably formed by the CDR sequences. Optionally, a Nanobody of the invention may also, and in addition to the at least one binding site for binding against Targets of the invention, contain one or more further binding sites for binding against other antigens, proteins or targets. For methods and positions for introducing such second binding sites, reference is for example made to Keck and Huston, Biophysical Journal, 71, October 1996, 2002-2011; EP 0 640 130 and WO 06/07260.

As generally described herein for the amino acid sequences of the invention, when a Nanobody of the invention (or a polypeptide of the invention comprising the same) is intended for administration to a subject (for example for therapeutic and/or diagnostic purposes as described herein), it is preferably directed against human Targets of the invention; whereas for veterinary purposes, it is preferably directed against Targets of the invention from the species to be treated. Also, as with the amino acid sequences of the invention, a Nanobody of the invention may or may not be cross-reactive (i.e. directed against Targets of the invention from two or more species of mammal, such as against human Targets of the invention and Targets of the invention from at least one of the species of mammal mentioned herein).

Also, again as generally described herein for the amino acid sequences of the invention, the Nanobodies of the invention may generally be directed against any antigenic determinant, epitope, part, domain, subunit or confirmation (where applicable) of Targets of the invention. However, it is generally assumed and preferred that the Nanobodies of the invention (and polypeptides comprising the same) are directed against and/or have been raised against at least one extracellular region, domain, loop or other extracellular epitope of one of the Targets of the invention (or a suitable peptide derived therefrom).

As already described herein, the amino acid sequence and structure of a Nanobody can be considered—without however being limited thereto—to be comprised of four framework regions or “FR's” (or sometimes also referred to as “FW's”), which are referred to in the art and herein as “Framework region 1” or “FR1”; as “Framework region 2” or “FR2”; as “Framework region 3” or “FR3”; and as “Framework region 4” or “FR4”, respectively; which framework regions are interrupted by three complementary determining regions or “CDR's”, which are referred to in the art as “Complementarity Determining Region 1” or “CDR1”; as “Complementarity Determining Region 2” or “CDR2”; and as “Complementarity Determining. Region 3” or “CDR3”, respectively. Some preferred framework sequences and CDR's (and combinations thereof) that are present in the Nanobodies of the invention are as described herein. Other suitable CDR sequences can be obtained by the methods described herein.

According to a non-limiting but preferred aspect of the invention, (the CDR sequences present in) the Nanobodies of the invention are such that:

-   -   the Nanobodies can bind to Targets of the invention with a         dissociation constant (K_(D)) of 10⁻⁵ to 10⁻¹² moles/liter or         less, and preferably 10⁻⁷ to 10⁻¹² moles/liter or less and more         preferably 10⁻⁸ to 10⁻¹² moles/liter (i.e. with an association         constant (K_(A)) of 10⁵ to 10¹² liter/moles or more, and         preferably 10⁷ to 10¹² liter/moles or more and more preferably         10⁸ to 10¹² liter/moles);         and/or such that:     -   the Nanobodies can bind to Targets of the invention with a         k_(on)-rate of between 10² M⁻¹s⁻¹ to about 10⁷ M⁻¹s⁻¹,         preferably between 10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more preferably         between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, such as between 10⁵ M⁻¹s⁻¹         and 10⁷ M⁻¹s⁻¹;         and/or such that they:     -   the Nanobodies can bind to Targets of the invention with a         k_(off) rate between 1 s⁻¹ (t_(1/2)=0.69 s) and 10⁻⁶ s⁻¹         (providing a near irreversible complex with a t_(1/2) of         multiple days), preferably between 10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more         preferably between 10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as between 10⁻⁴         s⁻¹ and 10⁻⁶ s⁻¹.

Preferably, (the CDR sequences present in) the Nanobodies of the invention are such that: a monovalent Nanobody of the invention (or a polypeptide that contains only one Nanobody of the invention) is preferably such that it will bind to Targets of the invention with an affinity less than 500 nM, preferably less than 200 nM, more preferably less than 10 nM, such as less than 500 pM.

The affinity of the Nanobody of the invention against Targets of the invention can be determined in a manner known per se, for example using the general techniques for measuring K_(D). K_(A), k_(off) or k_(on) mentioned herein, as well as some of the specific assays described herein.

Some preferred IC50 values for binding of the Nanobodies of the invention (and of polypeptides comprising the same) to Targets of the invention will become clear from the further description and examples herein.

In a preferred but non-limiting aspect, the invention relates to a Nanobody (as defined herein) against hCXCR4, which consists of 4 framework regions (FR1 to FR4 respectively) and 3 complementarity determining regions (CDR1 to CDR3 respectively), in which:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143;     and/or

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175;     and/or

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207;     or any suitable fragment of such an amino acid sequence.

In particular, according to this preferred but non-limiting aspect, the invention relates to a Nanobody (as defined herein) against human CXCR4, which consists of 4 framework regions (FR1 to FR4 respectively) and 3 complementarity determining regions (CDR1 to CDR3 respectively), in which:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more     preferably 142 to 143; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 142 to     157, more preferably 142 to 143;     and

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more     preferably 174 to 175; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 174 to     189, more preferably 174 to 175;     and

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more     preferably 206 to 207; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 206 to     221, more preferably 206 to 207;     or any suitable fragment of such an amino acid sequences.

In a preferred but non-limiting aspect, the invention relates to a Nanobody (as defined herein) against hCD4, which consists of 4 framework regions (FR1 to FR4 respectively) and 3 complementarity determining regions (CDR1 to CDR3 respectively), in which:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more     preferably 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287;     and/or

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more     preferably 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295;     and/or

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more     preferably 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303;     or any suitable fragment of such an amino acid sequence.

In particular, according to this preferred but non-limiting aspect, the invention relates to a Nanobody (as defined herein) against human CD4, which consists of 4 framework regions (FR1 to FR4 respectively) and 3 complementarity determining regions (CDR1 to CDR3 respectively), in which:

CDR1 is chosen from the group consisting of:

-   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more     preferably 287; -   b) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287; -   c) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 284 to     287, more preferably 287;     and

CDR2 is chosen from the group consisting of:

-   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more     preferably 295; -   e) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295; -   f) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 292 to     295, more preferably 295;     and

CDR3 is chosen from the group consisting of:

-   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more     preferably 303; -   h) amino acid sequences that have at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303; -   i) amino acid sequences that have 3, 2, or 1 amino acid difference     with at least one of the amino acid sequences of SEQ ID NO's: 300 to     303, more preferably 303;     or any suitable fragment of such an amino acid sequences.

As generally mentioned herein for the amino acid sequences of the invention, when a Nanobody of the invention contains one or more CDR1 sequences according to b) and/or c):

-   i) any amino acid substitution in such a CDR according to b)     and/or c) is preferably, and compared to the corresponding CDR     according to a), a conservative amino acid substitution (as defined     herein);     and/or -   ii) the CDR according to b) and/or c) preferably only contains amino     acid substitutions, and no amino acid deletions or insertions,     compared to the corresponding CDR according to a);     and/or -   iii) the CDR according to b) and/or c) may be a CDR that is derived     from a CDR according to a) by means of affinity maturation using one     or more techniques of affinity maturation known per se.

Similarly, when a Nanobody of the invention contains one or more CDR2 sequences according to e) and/or f):

-   i) any amino acid substitution in such a CDR according to e)     and/or f) is preferably, and compared to the corresponding CDR     according to d), a conservative amino acid substitution (as defined     herein);     and/or -   ii) the CDR according to e) and/or f) preferably only contains amino     acid substitutions, and no amino acid deletions or insertions,     compared to the corresponding CDR according to d);     and/or -   iii) the CDR according to e) and/or f) may be a CDR that is derived     from a CDR according to d) by means of affinity maturation using one     or more techniques of affinity maturation known per se.

Also, similarly, when a Nanobody of the invention contains one or more CDR3 sequences according to h) and/or i):

-   i) any amino acid substitution in such a CDR according to h)     and/or i) is preferably, and compared to the corresponding CDR     according to g), a conservative amino acid substitution (as defined     herein);     and/or -   ii) the CDR according to h) and/or i) preferably only contains amino     acid substitutions, and no amino acid deletions or insertions,     compared to the corresponding CDR according to g);     and/or -   iii) the CDR according to h) and/or i) may be a CDR that is derived     from a CDR according to g) by means of affinity maturation using one     or more techniques of affinity maturation known per se.

It should be understood that the last three paragraphs generally apply to any Nanobody of the invention that comprises one or more CDR1 sequences, CDR2 sequences and/or CDR3 sequences according to b), c), e), f), h) or i), respectively.

Of the Nanobodies of the invention, Nanobodies comprising one or more of the CDR's explicitly listed above are particularly preferred; Nanobodies comprising two or more of the CDR's explicitly listed above are more particularly preferred; and Nanobodies comprising three of the CDR's explicitly listed above are most particularly preferred.

Some particularly preferred, but non-limiting combinations of CDR sequences, as well as preferred combinations of CDR sequences and framework sequences, are mentioned in Table A-1 below, which lists the CDR sequences and framework sequences that are present in a number of preferred (but non-limiting) Nanobodies of the invention. As will be clear to the skilled person, a combination of CDR1, CDR2 and CDR3 sequences that occur in the same clone (i.e. CDR1, CDR2 and CDR3 sequences that are mentioned on the same line in Table A-1) will usually be preferred (although the invention in its broadest sense is not limited thereto, and also comprises other suitable combinations of the CDR sequences mentioned in Table A-1). Also, a combination of CDR sequences and framework sequences that occur in the same clone (i.e. CDR sequences and framework sequences that are mentioned on the same line in Table A-1) will usually be preferred (although the invention in its broadest sense is not limited thereto, and also comprises other suitable combinations of the CDR sequences and framework sequences mentioned in Table A-1, as well as combinations of such CDR sequences and other suitable framework sequences, e.g. as further described herein).

Also, in the Nanobodies of the invention that comprise the combinations of CDR's mentioned in Table A-1, each CDR can be replaced by a CDR chosen from the group consisting of amino acid sequences that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity (as defined herein) with the mentioned CDR's; in which:

-   i) any amino acid substitution in such a CDR is preferably, and     compared to the corresponding CDR sequence mentioned in Table A-1, a     conservative amino acid substitution (as defined herein);     and/or -   ii) any such CDR sequence preferably only contains amino acid     substitutions, and no amino acid deletions or insertions, compared     to the corresponding CDR sequence mentioned in Table A-1;     and/or -   iii) any such CDR sequence is a CDR that is derived by means of a     technique for affinity maturation known per se, and in particular     starting from the corresponding CDR sequence mentioned in Table A-1.

However, as will be clear to the skilled person, the (combinations of) CDR sequences, as well as (the combinations of) CDR sequences and framework sequences mentioned in Table A-1 will generally be preferred.

TABLE A-1 SEQ FR1 SEQ CDR1 SEQ FR2 SEQ CDR2 SEQ FR3 SEQ CDR3 SEQ FR4 (A) CDR's and framework sequences of Nanobodies against human CXCR4 126 EVQLVESGGG 142 SYAMS 158 WVRQAPG 174 GIKSSGDSTR 190 RFTISRDNAKNML 206 SRVSRTGL 222 RGQGTQ LVQTGGSLRL KGLEWVS YAGSVKG YLQMYSLKPEDTA YTYDN VTVSS SCAASGFTFS VYYCAK 127 EVQLVESGGG 143 NYAMG 159 WFRRAPG 175 AITRSGVRSG 191 RFTISRDNAKNTL 207 SAIGSGAL 223 SGQGTQ LVQAGGSLRL KEREFVA VSAIYGDSVK YLQMDSLKPDDTA RRFEYDY VTVSS SCAASGRTFN D VYTCAA 128 KVQLVESGGG 144 IHTMS 160 WVRQAPG 176 TIKPSGDTTN 192 RFTISRDNAKNTL 208 DYFGTGV 224 RGQGTQ LVQPGGSLRL KCPEWVS YANAVKG YLQMNSLKPEDTA VTVSS SCAASGFAFS VYYCAK 129 EVQLVESGGG 145 DYAMS 161 WVRQAPG 177 AISWNGGSTD 193 RFTISRDNAKNTL 209 DQGPEYSG 225 RGQGTQ LVQPGGSLRL KGLEWVS YADSVKG YLQMNSLKSEDTA TYYYTRQY VTVSS SCAASGFTFD EYYCAR GY 130 EVQLVESGGG 46 GYTIA 162 WFRQVPG 178 YHRWSDGANL 194 RFTISGHNAKNTV 210 APWITSND 226 WGQGTQ FVQAGGSLRL KEREFVA YADSVKG SLQMNSLKPEDTA KEYLY VTVSS SCETSGRPLL VYYCAA 131 EVQLVESGGG 147 DYATG 163 WFRKAPG 179 CISGSDGSTT 195 RPTISTDNAKNIV 211 QYGVGGRV 227 WGQGTQ LVQAGGSLRL KEREGVS YADSVKG YLEMNSLKPEDTA VCPCPYFY VTVSS ACAASGFTFE VYYCAQ DV 132 EVQLVESGGG 148 GYTIA 164 WFRQVPG 180 YHRWSDGANL 196 RFTISGHNAKNTV 212 AWIATTSND 228 WGQGTQ FVQAGGSLRL KEREFVA YADSVKG SLQMNSLKPEDTA KEYLY VTVSS SCETSGRPLL VYYCAA 133 EVQLVESGGG 149 PSAMA 165 WyRQGPG 181 STIWSRGETY 197 RFTISRDTANYTL 213 RVRPYGQY 229 WGQGTQ LVQAGGSLRL KERDFVA FADSVKG YLQMNNLKPEDTA DY VTVSS SCAASGLTFS VYYCSE 134 EVQLVESGGG 150 DYAMS 166 WVRQAPG 182 AISWNGGSAD 198 RFTISRDNAKNTL 214 DQGPFYSG 230 WGQGTQ LVQPGGSLRL KGLEWVS YADSVKG YLQMNSLKSEDTA TYYYTKGY VTVSS SCAASGFTFD VYYCAK Al 135 EVQLVESGGG 151 MG 167 WVRQAPG 183 TSRLITDNII 199 RFTLTRDNGKNTV 215 RQNYSRSV 231 WGQGTQ LAQAGGSLRL KEREFVT YADSVKG YLQMDSLKPDDTA FGAKDYDY VTVSS SCAASGRTYA VYYCAA 136 EVQLVESGGG 152 LNAMG 168 WVRQAPG 184 GITSSTSTYY 200 RFTISRDNTKNTV 216 DCPDYYSD 232 RGQGTQ LVQAGGSLRL KQRELVA ADSVKG YLQMNSLKPEDTA YECPLED VTVSS SCAASGSIFS VYYCNV 137 EVQLVESGGG 153 VNDMG 169 WYRQAPG 185 VITSGGGTNY 201 RFTISGDNRKKTV 217 YYSSGIST 233 WGQGTQ LAQPGGPLRL KQRELVA VDSVKG YLQMNSLKPEDTA LRS VTVSS TCEASGVIYS VYYCSI 138 EVQLVESGGG 154 YYTIG 170 WYRQAPG 186 CISSSDGSTA 202 RFTVSRDNAKNTV 218 BSADSRCS 234 WGQGTQ LVQAGGSLRL KEREGVS YLGSVQG YLQMNNLKPEDTA IGSIGFTW VTVSS SCEVSGFTRD VYYCAL LYNN 139 EVQLVESGGG 155 YEAIV 171 WLRQAPG 187 CITSRDSTTY 203 RFTISRDDAKETV 219 BTSMTCPT 235 RGQGTQ LVQPGGSLRL KELEGVS YASFVKG YLQMNNLKPEDTA LIVRFNY VTVSS SCAASSFIGN VYYCAV 140 EVQLVESGGG 156 NYAMG 172 WFRRAPG 188 AITRSGVRSG 204 RFTISRDNVKNTL 220 SAIGSGAL 236 SGQGTQ LVQAGGSLRL KEREFVA VSAIYGDSVK YLQMNTLKPEDTA RRFEYDY VTVSS SCKASGGTFN D VYYCAA 141 EVQLVESGGG 157 INAMG 173 WYRQAPG 189 SITSGGSTVY 205 RFTISRENYNTVY 221 DGVPEWGK 237 RGQGTQ LVQAGGSLRL KQRELVA ADSVKC LQMNSLKPEDTAV VQYPDTY VTVSS SCAASGSFFS YYCNA (B) CDR's and framework sequences of Nanobodies against human CD4 280 EVQLVESGGG 284 GYWMY 288 WVRQAPG 292 AISPCGGSTY 296 RFTISRDNAKNTL 300 SLTATHTY 304 WGQGTQ LVQAGGSLRL KCLEWVS YPDSVKG YLQMNSLKPEDTA EYDY VTVSS SCAASGFTFS LYYCAS 281 EVQLVESGGG 285 SYSMG 289 NFRQAPG 293 AISWSGDETS 297 RFTIARGNAKNTV 301 DRWWRPAG 305 WGQGTQ LVQAGGSLRL KEREFVA YADSVKG YLQMNSLKSEDTA LQWDY VTVSS SCAASGRTSA IYYCAG 282 EVQLVESGGG 286 FNAMG 290 WYRQAPG 294 TIARAGATKY 298 RFSISRDNAKNTV 302 RVFDLPND 306 WGQGTQ LVQAGGSLKL KQREWVT ADSVKG YLQMSSLKPODTA Y VTVSS SCAASRSILD TYYCNA 283 EVQLVESGGG 287 VMG 291 WERQAPG 295 AVRWSSTGIY 299 RFTISRDNAKNTV 303 DTYNSNPA 307 RGQGTQ SVQPGGSLTL KEREFVA YTQYADSVKS YLEMNSLKPEDTA RWDGYDF VTVSS SCGTSGRTFN VYYCAA

Thus, in the Nanobodies of the invention, at least one of the CDR1, CDR2 and CDR3 sequences present is suitably chosen from the group consisting of the CDR1. CDR2 and CDR3 sequences, respectively, listed in Table A-1; or from the group of CDR1, CDR2 and CDR3 sequences, respectively, that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% “sequence identity” (as defined herein) with at least one of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1; and/or from the group consisting of the CDR1, CDR2 and CDR3 sequences, respectively, that have 3, 2 or only 1 “amino acid difference(s)” (as defined herein) with at least one of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1.

In this context, by “suitably chosen” is meant that, as applicable, a CDR1 sequence is chosen from suitable CDR1 sequences (i.e. as defined herein), a CDR2 sequence is chosen from suitable CDR2 sequences (i.e. as defined herein), and a CDR3 sequence is chosen from suitable CDR3 sequence (i.e. as defined herein), respectively. More in particular, the CDR sequences are preferably chosen such that the Nanobodies of the invention bind to Targets of the invention with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein.

In particular, in the Nanobodies of the invention, at least the CDR3 sequence present is suitably chosen, from the group consisting of the CDR3 sequences listed in Table A-1 or from the group of CDR3 sequences that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with at least one of the CDR3 sequences listed in Table A-1; and/or from the group consisting of the CDR3 sequences that have 3, 2 or only 1 amino acid difference(s) with at least one of the CDR3 sequences listed in Table A-1.

Preferably, in the Nanobodies of the invention, at least two of the CDR1, CDR2 and CDR3 sequences present are suitably chosen from the group consisting of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1 or from the group consisting of CDR1, CDR2 and CDR3 sequences, respectively, that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with at least one of the CDR1. CDR2 and CDR3 sequences, respectively, listed in Table A-1; and/or from the group consisting of the CDR1, CDR2 and CDR3 sequences, respectively, that have 3, 2 or only 1 “amino acid difference(s)” with at least one of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1.

In particular, in the Nanobodies of the invention, at least the CDR3 sequence present is suitably chosen from the group consisting of the CDR3 sequences listed in Table A-1 or from the group of CDR3 sequences that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with at least one of the CDR3 sequences listed in Table A-1, respectively; and at least one of the CDR1 and CDR2 sequences present is suitably chosen from the group consisting of the CDR1 and CDR2 sequences, respectively, listed in Table A-1 or from the group of CDR1 and CDR2 sequences, respectively, that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with at least one of the CDR1 and CDR2 sequences, respectively, listed in Table A-1; and/or from the group consisting of the CDR1 and CDR2 sequences, respectively, that have 3, 2 or only 1 amino acid difference(s) with at least one of the CDR1 and CDR2 sequences, respectively, listed in Table A-1.

Most preferably, in the Nanobodies of the invention, all three CDR1, CDR2 and CDR3 sequences present are suitably chosen from the group consisting of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1 or from the group of CDR1, CDR2 and CDR3 sequences, respectively, that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with at least one of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1; and/or from the group consisting of the CDR1, CDR2 and CDR3 sequences, respectively, that have 3, 2 or only 1 amino acid difference(s) with at least one of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1.

Even more preferably, in the Nanobodies of the invention, at least one of the CDR1, CDR2 and CDR3 sequences present is suitably chosen from the group consisting of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1. Preferably, in this aspect, at least one or preferably both of the other two CDR sequences present are suitably chosen from CDR sequences that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with at least one of the corresponding CDR sequences, respectively, listed in Table A-1; and/or from the group consisting of the CDR sequences that have 3, 2 or only 1 amino acid difference(s) with at least one of the corresponding sequences, respectively, listed in Table A-1.

In particular, in the Nanobodies of the invention, at least the CDR3 sequence present is suitably chosen from the group consisting of the CDR3 listed in Table A-1. Preferably, in this aspect, at least one and preferably both of the CDR1 and CDR2 sequences present are suitably chosen from the groups of CDR1 and CDR2 sequences, respectively, that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with the CDR1 and CDR2 sequences, respectively, listed in Table A-1; and/or from the group consisting of the CDR1 and CDR2 sequences, respectively, that have 3, 2 or only 1 amino acid difference(s) with at least one of the CDR1 and CDR2 sequences, respectively, listed in Table A-1.

Even more preferably, in the Nanobodies of the invention, at least two of the CDR1, CDR2 and CDR3 sequences present are suitably chosen from the group consisting of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1. Preferably, in this aspect, the remaining CDR sequence present is suitably chosen from the group of CDR sequences that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with at least one of the corresponding CDR sequences listed in Table A-1; and/or from the group consisting of CDR sequences that have 3, 2 or only 1 amino acid difference(s) with at least one of the corresponding sequences listed in Table A-1.

In particular, in the Nanobodies of the invention, at least the CDR3 sequence is suitably chosen from the group consisting of the CDR3 sequences listed in Table A-1, and either the CDR1 sequence or the CDR2 sequence is suitably chosen from the group consisting of the CDR1 and CDR2 sequences, respectively, listed in Table A-1. Preferably, in this aspect, the remaining CDR sequence present is suitably chosen from the group of CDR sequences that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with at least one of the corresponding CDR sequences listed in Table A-1; and/or from the group consisting of CDR sequences that have 3, 2 or only 1 amino acid difference(s) with the corresponding CDR sequences listed in Table A-1.

Even more preferably, in the Nanobodies of the invention, all three CDR1, CDR2 and CDR3 sequences present are suitably chosen from the group consisting of the CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1.

Also, generally, the combinations of CDR's listed in Table A-1 (i.e. those mentioned on the same line in Table A-1) are preferred. Thus, it is generally preferred that, when a CDR in a Nanobody of the invention is a CDR sequence mentioned in Table A-1 or is suitably chosen from the group of CDR sequences that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with a CDR sequence listed in Table A-1; and/or from the group consisting of CDR sequences that have 3, 2 or only 1 amino acid difference(s) with a CDR sequence listed in Table A-1, that at least one and preferably both of the other CDR's are suitably chosen from the CDR sequences that belong to the same combination in Table A-1 (i.e. mentioned on the same line in Table A-1) or are suitably chosen from the group of CDR sequences that have at least 80%, preferably at least 90%, more preferably at least 95%, even more preferably at least 99% sequence identity with the CDR sequence(s) belonging to the same combination and/or from the group consisting of CDR sequences that have 3, 2 or only 1 amino acid difference(s) with the CDR sequence(s) belonging to the same combination. The other preferences indicated in the above paragraphs also apply to the combinations of CDR's mentioned in Table A-1.

Thus, by means of non-limiting examples, a Nanobody of the invention can for example comprise a CDR1 sequence that has more than 80% sequence identity with one of the CDR1 sequences mentioned in Table A-1, a CDR2 sequence that has 3, 2 or 1 amino acid difference with one of the CDR2 sequences mentioned in Table A-1 (but belonging to a different combination), and a CDR3 sequence.

Some preferred Nanobodies of the invention may for example comprise: (1) a CDR1 sequence that has more than 80% sequence identity with one of the CDR1 sequences mentioned in Table A-1; a CDR2 sequence that has 3, 2 or 1 amino acid difference with one of the CDR2 sequences mentioned in Table A-1 (but belonging to a different combination); and a CDR3 sequence that has more than 80% sequence identity with one of the CDR3 sequences mentioned in Table A-1 (but belonging to a different combination); or (2) a CDR1 sequence that has more than 80% sequence identity with one of the CDR1 sequences mentioned in Table A-1; a CDR2 sequence, and one of the CDR3 sequences listed in Table A-1; or (3) a CDR1 sequence; a CDR2 sequence that has more than 80% sequence identity with one of the CDR2 sequence listed in Table A-1; and a CDR3 sequence that has 3, 2 or 1 amino acid differences with the CDR3 sequence mentioned in Table A-1 that belongs to the same combination as the CDR2 sequence.

Some particularly preferred Nanobodies of the invention may for example comprise: (1) a CDR1 sequence that has more than 80% sequence identity with one of the CDR1 sequences mentioned in Table A-1; a CDR2 sequence that has 3, 2 or 1 amino acid difference with the CDR2 sequence mentioned in Table A-1 that belongs to the same combination; and a CDR3 sequence that has more than 80% sequence identity with the CDR3 sequence mentioned in Table A-1 that belongs to the same combination; (2) a CDR1 sequence; a CDR 2 listed in Table A-1 and a CDR3 sequence listed in Table A-1 (in which the CDR2 sequence and CDR3 sequence may belong to different combinations).

Some even more preferred Nanobodies of the invention may for example comprise: (1) a CDR1 sequence that has more than 80% sequence identity with one of the CDR1 sequences mentioned in Table A-1; the CDR2 sequence listed in Table A-1 that belongs to the same combination; and a CDR3 sequence mentioned in Table A-1 that belongs to a different combination; or (2) a CDR1 sequence mentioned in Table A-1; a CDR2 sequence that has 3, 2 or 1 amino acid differences with the CDR2 sequence mentioned in Table A-1 that belongs to the same combination; and a CDR3 sequence that has more than 80% sequence identity with the CDR3 sequence listed in Table A-1 that belongs to the same or a different combination.

Particularly preferred Nanobodies of the invention may for example comprise a CDR1 sequence mentioned in Table A-1, a CDR2 sequence that has more than 80% sequence identity with the CDR2 sequence mentioned in Table A-1 that belongs to the same combination; and the CDR3 sequence mentioned in Table A-1 that belongs to the same combination.

In the most preferred Nanobodies of the invention, the CDR1, CDR2 and CDR3 sequences present are suitably chosen from one of the combinations of CDR1, CDR2 and CDR3 sequences, respectively, listed in Table A-1.

According to another preferred, but non-limiting aspect of the invention (a) CDR1 has a length of between 1 and 12 amino acid residues, and usually between 2 and 9 amino acid residues, such as 5, 6 or 7 amino acid residues; and/or (b) CDR2 has a length of between 13 and 24 amino acid residues, and usually between 15 and 21 amino acid residues, such as 16 and 17 amino acid residues; and/or (c) CDR3 has a length of between 2 and 35 amino acid residues, and usually between 3 and 30 amino acid residues, such as between 6 and 23 amino acid residues.

In another preferred, but non-limiting aspect, the invention relates to a Nanobody in which the CDR sequences (as defined herein) have more than 80%, preferably more than 90%, more preferably more than 95%, such as 99% or more sequence identity (as defined herein) with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239, and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311.

Generally, Nanobodies with the above CDR sequences may be as further described herein, and preferably have framework sequences that are also as further described herein. Thus, for example and as mentioned herein, such Nanobodies may be naturally occurring Nanobodies (from any suitable species), naturally occurring V_(HH) sequences (i.e. from a suitable species of Camelid) or synthetic or semi-synthetic amino acid sequences or Nanobodies, including but not limited to partially humanized Nanobodies or V_(HH) sequences, fully humanized Nanobodies or V_(HH) sequences, camelized heavy chain variable domain sequences, as well as Nanobodies that have been obtained by the techniques mentioned herein.

Thus, in one specific, but non-limiting aspect, the invention relates to a humanized Nanobody, which consists of 4 framework regions (FR1 to FR4 respectively) and 3 complementarity determining regions (CDR1 to CDR3 respectively), in which CDR1 to CDR3 are as defined herein and in which said humanized Nanobody comprises at least one humanizing substitution (as defined herein), and in particular at least one humanizing substitution in at least one of its framework sequences (as defined herein).

In another preferred, but non-limiting aspect, the invention relates to a Nanobody in which the CDR sequences have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said Nanobody and one or more of the sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239, and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311, in which the amino acid residues that form the framework regions are disregarded. Such Nanobodies can be as further described herein.

In another preferred, but non-limiting aspect, the invention relates to a Nanobody with an amino acid sequence that is chosen from the group consisting of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311 or from the group consisting of from amino acid sequences that have more than 80%, preferably more than 90%, more preferably more than 95%, such as 99% or more sequence identity (as defined herein) with at least one of the amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311.

Another preferred, but non-limiting aspect of the invention relates to humanized variants of the Nanobodies of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311, that comprise, compared to the corresponding native V_(HH) sequence, at least one humanizing substitution (as defined herein), and in particular at least one humanizing substitution in at least one of its framework sequences (as defined herein).

The polypeptides of the invention comprise or essentially consist of at least one Nanobody of the invention. Thus in another preferred, but non-limiting aspect, the invention relates to a polypeptide comprise or essentially consist of at least one Nanobody that is chosen from the group consisting of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311 or from the group consisting of amino acid sequences that have more than 80%, preferably more than 90%, more preferably more than 95%, such as 99% or more sequence identity (as defined herein) with at least one of the amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311. Thus in another preferred, but non-limiting aspect, the invention relates to a polypeptide comprise or essentially consist of amino acid sequences of SEQ ID NO's: 261 to 264, more preferably SEQ ID NO: 263 to 264.

It will be clear to the skilled person that the Nanobodies that are mentioned herein as “preferred” (or “more preferred”, “even more preferred”, etc.) are also preferred (or more preferred, or even more preferred, etc.) for use in the polypeptides described herein. Thus, polypeptides that comprise or essentially consist of one or more “preferred” Nanobodies of the invention will generally be preferred, and polypeptides that comprise or essentially consist of one or more “more preferred” Nanobodies of the invention will generally be more preferred, etc.

Generally, proteins or polypeptides that comprise or essentially consist of a single Nanobody (such as a single Nanobody of the invention) will be referred to herein as “monovalent” proteins or polypeptides or as “monovalent constructs”. Proteins and polypeptides that comprise or essentially consist of two or more Nanobodies (such as at least two Nanobodies of the invention or at least one Nanobody of the invention and at least one other Nanobody) will be referred to herein as “multivalent” proteins or polypeptides or as “multivalent constructs”, and these may provide certain advantages compared to the corresponding monovalent Nanobodies of the invention. Some non-limiting examples of such multivalent constructs will become clear from the further description herein.

According to one specific, but non-limiting aspect, a polypeptide of the invention comprises or essentially consists of at least two Nanobodies of the invention, such as two or three Nanobodies of the invention. As further described herein, such multivalent constructs can provide certain advantages compared to a protein or polypeptide comprising or essentially consisting of a single Nanobody of the invention, such as a much improved avidity for Targets of the invention. Such multivalent constructs will be clear to the skilled person based on the disclosure herein, and e.g. are polypeptides that comprise or essentially consist of amino acid sequences of SEQ ID NO: 261 to 266.

According to another specific, but non-limiting aspect, a polypeptide of the invention comprises or essentially consists of at least one Nanobody of the invention and at least one other binding unit (i.e. directed against another epitope, antigen, target, protein or polypeptide), which is preferably also a Nanobody. Such proteins or polypeptides are also referred to herein as “multispecific” proteins or polypeptides or as ‘multispecific constructs”, and these may provide certain advantages compared to the corresponding monovalent Nanobodies of the invention (as will become clear from the further discussion herein of some preferred, but-nonlimiting multispecific constructs). Such multispecific constructs will be clear to the skilled person based on the disclosure herein, and e.g. are polypeptides that comprise or essentially consist of amino acid sequences of SEQ ID NO: 263 to 264.

According to yet another specific, but non-limiting aspect, a polypeptide of the invention comprises or essentially consists of at least one Nanobody of the invention, optionally one or more further Nanobodies, and at least one other amino acid sequence (such as a protein or polypeptide) that confers at least one desired property to the Nanobody of the invention and/or to the resulting fusion protein. Again, such fusion proteins may provide certain advantages compared to the corresponding monovalent Nanobodies of the invention. Some non-limiting examples of such amino acid sequences and of such fusion constructs will become clear from the further description herein.

It is also possible to combine two or more of the above aspects, for example to provide a trivalent bispecific construct comprising two Nanobodies of the invention and one other Nanobody, and optionally one or more other amino acid sequences. Further non-limiting examples of such constructs, as well as some constructs that are particularly preferred within the context of the present invention, will become clear from the further description herein.

In the above constructs, the one or more Nanobodies and/or other amino acid sequences may be directly linked to each other and/or suitably linked to each other via one or more linker sequences. Some suitable but non-limiting examples of such linkers will become clear from the further description herein.

In one specific aspect of the invention, a Nanobody of the invention or a compound, construct or polypeptide of the invention comprising at least one Nanobody of the invention may have an increased half-life, compared to the corresponding amino acid sequence of the invention. Some preferred, but non-limiting examples of such Nanobodies, compounds and polypeptides will become clear to the skilled person based on the further disclosure herein, and for example comprise Nanobodies sequences or polypeptides of the invention that have been chemically modified to increase the half-life thereof (for example, by means of pegylation); amino acid sequences of the invention that comprise at least one additional binding site for binding to a serum protein (such as serum albumin); or polypeptides of the invention that comprise at least one Nanobody of the invention that is linked to at least one moiety (and in particular at least one amino acid sequence) that increases the half-life of the Nanobody of the invention. Examples of polypeptides of the invention that comprise such half-life extending moieties or amino acid sequences will become clear to the skilled person based on the further disclosure herein; and for example include, without limitation, polypeptides in which the one or more Nanobodies of the invention are suitable linked to one or more serum proteins or fragments thereof (such as serum albumin or suitable fragments thereof) or to one or more binding units that can bind to serum proteins (such as, for example, Nanobodies or (single) domain antibodies that can bind to serum proteins such as serum albumin, serum immunoglobulins such as IgG, or transferrin); polypeptides in which a Nanobody of the invention is linked to an Fc portion (such as a human Fc) or a suitable part or fragment thereof; or polypeptides in which the one or more Nanobodies of the invention are suitable linked to one or more small proteins or peptides that can bind to serum proteins (such as, without limitation, the proteins and peptides described in WO 91/01743, WO 01/45746, WO 02/076489 and to WO 08/068280.

Again, as will be clear to the skilled person, such Nanobodies, compounds, constructs or polypeptides may contain one or more additional groups, residues, moieties or binding units, such as one or more further amino acid sequences and in particular one or more additional Nanobodies (i.e. not directed against Targets of the invention), so as to provide a tri- of multispecific Nanobody construct.

Generally, the Nanobodies of the invention (or compounds, constructs or polypeptides comprising the same) with increased half-life preferably have a half-life that is at least 1.5 times, preferably at least 2 times, such as at least 5 times, for example at least 10 times or more than 20 times, greater than the half-life of the corresponding amino acid sequence of the invention per se. For example, the Nanobodies, compounds, constructs or polypeptides of the invention with increased half-life may have a half-life that is increased with more than 1 hours, preferably more than 2 hours, more preferably more than 6 hours, such as more than 12 hours, or even more than 24, 48 or 72 hours, compared to the corresponding amino acid sequence of the invention per se.

In a preferred, but non-limiting aspect of the invention, such Nanobodies, compound, constructs or polypeptides of the invention exhibit a serum half-life in human of at least about 12 hours, preferably at least 24 hours, more preferably at least 48 hours, even more preferably at least 72 hours or more. For example, compounds or polypeptides of the invention may have a half-life of at least 5 days (such as about 5 to 10 days), preferably at least 9 days (such as about 9 to 14 days), more preferably at least about 10 days (such as about 10 to 15 days), or at least about 11 days (such as about 11 to 16 days), more preferably at least about 12 days (such as about 12 to 18 days or more), or more than 14 days (such as about 14 to 19 days).

In another one aspect of the invention, a polypeptide of the invention comprises one or more (such as two or preferably one) Nanobodies of the invention linked (optionally via one or more suitable linker sequences) to one or more (such as two and preferably one) amino acid sequences that allow the resulting polypeptide of the invention to cross the blood brain barrier. In particular, said one or more amino acid sequences that allow the resulting polypeptides of the invention to cross the blood brain barrier may be one or more (such as two and preferably one) Nanobodies, such as the Nanobodies described in WO 02/057445, of which FC44 (SEQ ID NO: 189 of WO 06/040153) and FC5 (SEQ ID NO: 190 of WO 06/040154) are preferred examples.

In particular, polypeptides comprising one or more Nanobodies of the invention are preferably such that they:

-   -   bind to Targets of the invention with a dissociation constant         (K_(D)) of 10⁻⁵ to 10⁻¹² moles/liter or less, and preferably         10⁻⁷ to 10⁻¹² moles/liter or less and more preferably 10⁻⁸ to         10⁻¹² moles/liter (i.e. with an association constant (K_(A)) of         10⁵ to 10¹² liter/moles or more, and preferably 10⁷ to 10¹²         liter/moles or more and more preferably 10⁸ to 10¹²         liter/moles);         and/or such that they:     -   bind to Targets of the invention with a k_(on)-rate of between         10² M⁻¹s⁻¹ to about 10⁷ M⁻¹s⁻¹ preferably between 10³ M⁻¹s⁻¹ and         10⁷ M⁻¹s⁻¹, more preferably between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹,         such as between 10⁵ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹;         and/or such that they:     -   bind to Targets of the invention with a k_(off) rate between 1         s⁻¹ (t_(1/2)=0.69 s) and 10⁻⁶ s⁻¹ (providing a near irreversible         complex with a t_(1/2) of multiple days), preferably between         10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more preferably between 10⁻³ s⁻¹ and 10⁻⁶         s⁻¹, such as between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹.

Preferably, a polypeptide that contains only one amino acid sequence of the invention is preferably such that it will bind to Targets of the invention with an affinity less than 500 nM, preferably less than 200 nM, more preferably less than 10 nM, such as less than 500 pM. In this respect, it will be clear to the skilled person that a polypeptide that contains two or more Nanobodies of the invention may bind to Targets of the invention with an increased avidity, compared to a polypeptide that contains only one amino acid sequence of the invention.

Some preferred IC₅₀ values for binding of the amino acid sequences or polypeptides of the invention to Targets of the invention will become clear from the further description and examples herein.

Another aspect of this invention relates to a nucleic acid that encodes an amino acid sequence of the invention (such as a Nanobody of the invention) or a polypeptide of the invention comprising the same. Again, as generally described herein for the nucleic acids of the invention, such a nucleic acid may be in the form of a genetic construct, as defined herein.

In another aspect, the invention relates to host or host cell that expresses or that is capable of expressing an amino acid sequence (such as a Nanobody) of the invention and/or a polypeptide of the invention comprising the same; and/or that contains a nucleic acid of the invention. Some preferred but non-limiting examples of such hosts or host cells will become clear from the further description herein.

Another aspect of the invention relates to a product or composition containing or comprising at least one amino acid sequence of the invention, at least one polypeptide of the invention and/or at least one nucleic acid of the invention, and optionally one or more further components of such compositions known per se, i.e. depending on the intended use of the composition. Such a product or composition may for example be a pharmaceutical composition (as described herein), a veterinary composition or a product or composition for diagnostic use (as also described herein). Some preferred but non-limiting examples of such products or compositions will become clear from the further description herein.

The invention further relates to methods for preparing or generating the amino acid sequences, compounds, constructs, polypeptides, nucleic acids, host cells, products and compositions described herein. Some preferred but non-limiting examples of such methods will become clear from the further description herein.

The invention further relates to applications and uses of the amino acid sequences, compounds, constructs, polypeptides, nucleic acids, host cells, products and compositions described herein, as well as to methods for the prevention and/or treatment for diseases and disorders associated with Targets of the invention. Some preferred but non-limiting applications and uses will become clear from the further description herein.

Other aspects, embodiments, advantages and applications of the invention will also become clear from the further description hereinbelow.

Generally, it should be noted that the term. Nanobody as used herein in its broadest sense is not limited to a specific biological source or to a specific method of preparation. For example, as will be discussed in more detail below, the Nanobodies of the invention can generally be obtained: (1) by isolating the V_(HH) domain of a naturally occurring heavy chain antibody; (2) by expression of a nucleotide sequence encoding a naturally occurring V_(HH) domain; (3) by “humanization” (as described herein) of a naturally occurring V_(HH) domain or by expression of a nucleic acid encoding a such humanized V_(HH) domain; (4) by “camelization” (as described herein) of a naturally occurring V_(H) domain from any animal species, and in particular a from species of mammal, such as from a human being, or by expression of a nucleic acid encoding such a camelized V_(H) domain; (5) by “camelisation” of a “domain antibody” or “Dab” as described by Ward et al (supra), or by expression of a nucleic acid encoding such a camelized V_(H) domain; (6) by using synthetic or semi-synthetic techniques for preparing proteins, polypeptides or other amino acid sequences known per se; (7) by preparing a nucleic acid encoding a Nanobody using techniques for nucleic acid synthesis known per se, followed by expression of the nucleic acid thus obtained; and/or (8) by any combination of one or more of the foregoing. Suitable methods and techniques for performing the foregoing will be clear to the skilled person based on the disclosure herein and for example include the methods and techniques described in more detail herein.

One preferred class of Nanobodies corresponds to the V_(HH) domains of naturally occurring heavy chain antibodies directed against Targets of the invention. As further described herein, such V_(HH) sequences can generally be generated or obtained by suitably immunizing a species of Camelid with Targets of the invention (i.e. so as to raise an immune response and/or heavy chain antibodies directed against Targets of the invention), by obtaining a suitable biological sample from said Camelid (such as a blood sample, serum sample or sample of B-cells), and by generating V_(HH) sequences directed against Targets of the invention, starting from said sample, using any suitable technique known per se. Such techniques will be clear to the skilled person and/or are further described herein.

Alternatively, such naturally occurring V_(HH) domains against Targets of the invention, can be obtained from naïve libraries of Camelid V_(HH) sequences, for example by screening such a library using Targets of the invention, or at least one part, fragment, antigenic determinant or epitope thereof using one or more screening techniques known per se. Such libraries and techniques are for example described in WO 99/37681, WO 01/90190, WO 03/025020 and WO 03/035694. Alternatively, improved synthetic or semi-synthetic libraries derived from naïve V_(HH) libraries may be used, such as V_(HH) libraries obtained from naïve V_(HH) libraries by techniques such as random mutagenesis and/or CDR shuffling, as for example described in WO 00/43507.

Thus, in another aspect, the invention relates to a method for generating Nanobodies, that are directed against Targets of the invention. In one aspect, said method at least comprises the steps of:

-   a) providing a set, collection or library of Nanobody sequences; and -   b) screening said set, collection or library of Nanobody sequences     for Nanobody sequences that can bind to and/or have affinity for     Targets of the invention;     and -   c) isolating the Nanobody or Nanobodies that can bind to and/or have     affinity for Targets of the invention.

In such a method, the set, collection or library of Nanobody sequences may be a naïve set, collection or library of Nanobody sequences; a synthetic or semi-synthetic set, collection or library of Nanobody sequences; and/or a set, collection or library of Nanobody sequences that have been subjected to affinity maturation.

In a preferred aspect of this method, the set, collection or library of Nanobody sequences may be an immune set, collection or library of Nanobody sequences, and in particular an immune set, collection or library of V_(HH) sequences, that have been derived from a species of Camelid that has been suitably immunized with Targets of the invention or with a suitable antigenic determinant based thereon or derived therefrom, such as an antigenic part, fragment, region, domain, loop or other epitope thereof. In one particular aspect, said antigenic determinant may be an extracellular part, region, domain, loop or other extracellular epitope(s).

In the above methods, the set, collection or library of Nanobody or V_(HH) sequences may be displayed on a phage, phagemid, ribosome or suitable micro-organism (such as yeast), such as to facilitate screening. Suitable methods, techniques and host organisms for displaying and screening (a set, collection or library of) Nanobody sequences will be clear to the person skilled in the art, for example on the basis of the further disclosure herein. Reference is also made to WO 03/054016 and to the review by Hoogenboom in Nature Biotechnology, 23, 9, 1105-1116 (2005).

In another aspect, the method for generating Nanobody sequences comprises at least the steps of:

-   a) providing a collection or sample of cells derived from a species     of Camelid that express immunoglobulin sequences; -   b) screening said collection or sample of cells for (i) cells that     express an immunoglobulin sequence that can bind to and/or have     affinity for Targets of the invention; and (ii) cells that express     heavy chain antibodies, in which substeps (i) and (ii) can be     performed essentially as a single screening step or in any suitable     order as two separate screening steps, so as to provide at least one     cell that expresses a heavy chain antibody that can bind to and/or     has affinity for Targets of the invention;     and -   c) either (i) isolating from said cell the V_(HH) sequence present     in said heavy chain antibody; or (ii) isolating from said cell a     nucleic acid sequence that encodes the V_(HH) sequence present in     said heavy chain antibody, followed by expressing said V_(HH)     domain.

In another aspect, the method for generating Nanobody sequences directed against at least one of the Targets of the invention, comprises at least the steps of:

-   a. a step of suitably immunizing a Camelid with a suitable antigen     that comprises the desired extracellular part, region, domain, loop     or other extracellular epitope(s), or with a suitable peptide     derived therefrom or based thereon, such that an immune response     against the desired extracellular part, region, domain, loop or     other extracellular epitope(s) is raised. The antigen may be any     suitable antigen that is capable of raising an immune response     against the desired extracellular part, region, domain, loop or     other extracellular epitope(s); such as, for example and without     limitation, whole cells that are alive and overexpress the desired     extracellular part, region, domain, loop or other extracellular     epitope(s) on their surface in their native confirmation, cell wall     fragments thereof or any other suitable preparation derived from     such cells, vesicles that have the desired extracellular part,     region, domain, loop or other extracellular epitope(s) on their     surface, a subunit or fragment of a subunit of a Target of the     invention, e.g. human CXCR4 or hCD4, that comprises the desired     extracellular part, region, domain, loop or other extracellular     epitope(s), or a synthetic or semi-synthetic peptide that comprises     and/or is based on (the amino acid sequence of) the desired     extracellular part, region, domain, loop or other extracellular     epitope(s), more preferably, whole cells (e.g. HEK293) that are     alive and overexpress the desired extracellular part, region,     domain, loop or other extracellular epitope(s) on their surface in     their native confirmation; and -   b. a step of selection for binding for the desired extracellular     part, region, domain, loop or other extracellular epitope(s) using     cell membranes preparation of different (than the one using in     immunization) and several cell types overexpressing said Target of     the invention, e.g. human CXCR4. This may for example be performed     by selecting from a set, a collection or a library of cells that     express heavy chain antibodies on their surface (e.g. B-cells     obtained from a suitably immunized Camelid) and using a cell     membranes preparation of e.g. a first type of cells such as e.g. CHO     for a first round selection and e.g. a second type of cells such as     e.g. COS-7 cells for a second round selection, by selecting from a     (naïve or immune) library of VHH sequences or Nanobody sequences by     using a cell membranes preparation of e.g. a first type of cell such     as e.g. CHO for a first round selection and e.g. a second type of     cell such as e.g. COS-7 cell for a second round selection, or by     selecting from a (naïve or immune) library of nucleic acid sequences     that encode VHH sequences or Nanobody sequences by using a cell     membranes preparation of e.g. a first type of cell such as e.g. CHO     for a first round selection and e.g. a second type of cells such as     e.g. COS-7 cell for a second round selection; which may all be     performed in a manner known per se; and optionally -   c. washing only mildly with a buffer such as PBS without detergents;     and which method may optionally further comprise one or more other     suitable steps known per se, such as, for example and without     limitation, a step of affinity maturation, a step of expressing the     desired amino acid sequence, a step of screening for binding and/or     for activity against the desired antigen (in this case, the Target     of the invention, e.g. human CXCR4 or hCD4), a step of determining     the desired amino acid sequence or nucleotide sequence, a step of     introducing one or more humanizing substitutions (e.g. as further     described herein), a step of formatting in a suitable multivalent     and/or multispecific format, a step of screening for the desired     biological and/or physiological properties (i.e. using a suitable     assay, such as those described herein); and/or any suitable     combination of one or more of such steps, in any suitable order.

In another aspect, the method for generating Nanobody sequences directed against a transmembranal protein comprises at least the steps of:

-   a. a step of suitably immunizing a Camelid with a suitable antigen     that comprises the desired extracellular part, region, domain, loop     or other extracellular epitope(s), or with a suitable peptide     derived therefrom or based thereon, such that an immune response     against the desired extracellular part, region, domain, loop or     other extracellular epitope(s) is raised. The antigen may be any     suitable antigen that is capable of raising an immune response     against the desired extracellular part, region, domain, loop or     other extracellular epitope(s); such as, for example and without     limitation, whole cells that are alive and overexpress the desired     extracellular part, region, domain, loop or other extracellular     epitope(s) on their surface in their native confirmation, cell wall     fragments thereof or any other suitable preparation derived from     such cells, vesicles that have the desired extracellular part,     region, domain, loop or other extracellular epitope(s) on their     surface, a subunit or fragment of a subunit of a transmembrane     protein, in particular multiple spanning transmembrane protein for     which the native conformation cannot be reproduced in other “in     vitro” system (at least at time of filing of this application), that     comprises the desired extracellular part, region, domain, loop or     other extracellular epitope(s), or a synthetic or semi-synthetic     peptide that comprises and/or is based on (the amino acid sequence     of) the desired extracellular part, region, domain, loop or other     extracellular epitope(s), more preferably, whole cells (e.g. HEK293)     that are alive and overexpress the desired extracellular part,     region, domain, loop or other extracellular epitope(s) on their     surface in their native confirmation; and -   b. a step of selection for binding for the desired extracellular     part, region, domain, loop or other extracellular epitope(s) using     cell membranes preparation of different (than the one using in     immunization) and several cell types overexpressing said     transmembrane protein, in particular multiple spanning transmembrane     protein for which the native conformation cannot be reproduced in     other “in vitro” system (at least at time of filing of this     application). This may for example be performed by selecting from a     set, a collection or a library of cells that express heavy chain     antibodies on their surface (e.g. B-cells obtained from a suitably     immunized Camelid) and using a cell membranes preparation of e.g. a     first type of cells such as e.g. CHO for a first round selection and     e.g. a second type of cells such as e.g. COS-7 cells for a second     round selection, by selecting from a (naïve or immune) library of     VHH sequences or Nanobody sequences by using a cell membranes     preparation of e.g. a first type of cell such as e.g. CHO for a     first round selection and e.g. a second type of cell such as e.g.     COS-7 cell for a second round selection, or by selecting from a     (naïve or immune) library of nucleic acid sequences that encode VHH     sequences or Nanobody sequences by using a cell membranes     preparation of e.g. a first type of cell such as e.g. CHO for a     first round selection and e.g. a second type of cells such as e.g.     COS-7 cell for a second round selection; which may all be performed     in a manner known per se; and optionally -   c. washing only mildly with a buffer such as PBS without detergents;     and which method may optionally further comprise one or more other     suitable steps known per se, such as, for example and without     limitation, a step of affinity maturation, a step of expressing the     desired amino acid sequence, a step of screening for binding and/or     for activity against the desired antigen (in this case, the     transmebrane protein), a step of determining the desired amino acid     sequence or nucleotide sequence, a step of introducing one or more     humanizing substitutions (e.g. as further described herein), a step     of formatting in a suitable multivalent and/or multispecific format,     a step of screening for the desired biological and/or physiological     properties (i.e. using a suitable assay, such as those described     herein); and/or any suitable combination of one or more of such     steps, in any suitable order.

In the method according to this aspect, the collection or sample of cells may for example be a collection or sample of B-cells.

Also, in this method, the sample of cells may be derived from a Camelid that has been suitably immunized with Targets of the invention or a suitable antigenic determinant based thereon or derived therefrom, such as an antigenic part, fragment, region, domain, loop or other epitope thereof. In one particular aspect, said antigenic determinant may be an extracellular part, region, domain, loop or other extracellular epitope(s).

The above method may be performed in any suitable manner, as will be clear to the skilled person. Reference is for example made to EP 0 542 810, WO 05/19824, WO 04/051268 and WO 04/106377. The screening of step b) is preferably performed using a flow cytometry technique such as FACS. For this, reference is for example made to Lieby et al., Blood, Vol. 97, No. 12, 3820. Particular reference is made to the so-called “Nanoclone” technique described in International application WO 06/079372 by Ablynx N.V.

In another aspect, the method for generating an amino acid sequence directed against Targets of the invention may comprise at least the steps of:

-   a) providing a set, collection or library of nucleic acid sequences     encoding heavy chain antibodies or Nanobody sequences; -   b) screening said set, collection or library of nucleic acid     sequences for nucleic acid sequences that encode a heavy chain     antibody or a Nanobody sequence that can bind to and/or has affinity     for Targets of the invention;     and -   c) isolating said nucleic acid sequence, followed by expressing the     V_(HH) sequence present in said heavy chain antibody or by     expressing said Nanobody sequence, respectively.

In such a method, the set, collection or library of nucleic acid sequences encoding heavy chain antibodies or Nanobody sequences may for example be a set, collection or library of nucleic acid sequences encoding a naïve set, collection or library of heavy chain antibodies or V_(HH) sequences; a set, collection or library of nucleic acid sequences encoding a synthetic or semi-synthetic set, collection or library of Nanobody sequences; and/or a set, collection or library of nucleic acid sequences encoding a set, collection or library of Nanobody sequences that have been subjected to affinity maturation.

In a preferred aspect of this method, the set, collection or library of nucleic acid sequences may be an immune set, collection or library of nucleic acid sequences encoding heavy chain antibodies or V_(HH) sequences derived from a Camelid that has been suitably immunized with Targets of the invention or with a suitable antigenic determinant based thereon or derived therefrom, such as an antigenic part, fragment, region, domain, loop or other epitope thereof. In one particular aspect, said antigenic determinant may be an extracellular part, region, domain, loop or other extracellular epitope(s).

In the above methods, the set, collection or library of nucleotide sequences may be displayed on a phage, phagemid, ribosome or suitable micro-organism (such as yeast), such as to facilitate screening. Suitable methods, techniques and host organisms for displaying and screening (a set, collection or library of) nucleotide sequences encoding amino acid sequences will be clear to the person skilled in the art, for example on the basis of the further disclosure herein. Reference is also made to WO 03/054016 and to the review by Hoogenboom in Nature Biotechnology, 23, 9, 1105-1116 (2005).

As will be clear to the skilled person, the screening step of the methods described herein can also be performed as a selection step. Accordingly the term “screening” as used in the present description can comprise selection, screening or any suitable combination of selection and/or screening techniques. Also, when a set, collection or library of sequences is used, it may contain any suitable number of sequences, such as 1, 2, 3 or about 5, 10, 50, 100, 500, 1000, 5000, 10⁴, 10⁵, 10⁶, 10⁷, 10⁸ or more sequences.

Also, one or more or all of the sequences in the above set, collection or library of amino acid sequences may be obtained or defined by rational, or semi-empirical approaches such as computer modelling techniques or biostatics or datamining techniques.

Furthermore, such a set, collection or library can comprise one, two or more sequences that are variants from one another (e.g. with designed point mutations or with randomized positions), compromise multiple sequences derived from a diverse set of naturally diversified sequences (e.g. an immune library)), or any other source of diverse sequences (as described for example in Hoogenboom et al, Nat Biotechnol 23:1105, 2005 and Binz et al, Nat Biotechnol 2005, 23:1247). Such set, collection or library of sequences can be displayed on the surface of a phage particle, a ribosome, a bacterium, a yeast cell, a mammalian cell, and linked to the nucleotide sequence encoding the amino acid sequence within these carriers. This makes such set, collection or library amenable to selection procedures to isolate the desired amino acid sequences of the invention. More generally, when a sequence is displayed on a suitable host or host cell, it is also possible (and customary) to first isolate from said host or host cell a nucleotide sequence that encodes the desired sequence, and then to obtain the desired sequence by suitably expressing said nucleotide sequence in a suitable host organism. Again, this can be performed in any suitable manner known per se, as will be clear to the skilled person.

Yet another technique for obtaining V_(HH) sequences or Nanobody sequences directed against Targets of the invention involves suitably immunizing a transgenic mammal that is capable of expressing heavy chain antibodies (i.e. so as to raise an immune response and/or heavy chain antibodies directed against Targets of the invention), obtaining a suitable biological sample from said transgenic mammal that contains (nucleic acid sequences encoding) said V_(HH) sequences or Nanobody sequences (such as a blood sample, serum sample or sample of B-cells), and then generating V_(HH) sequences directed against Targets of the invention, starting from said sample, using any suitable technique known per se (such as any of the methods described herein or a hybridoma technique). For example, for this purpose, the heavy chain antibody-expressing mice and the further methods and techniques described in WO 02/085945, WO 04/049794 and WO 06/008548 and Janssens et al., Proc. Natl. Acad. Sci. USA. 2006 Oct. 10; 103(41):15130-5 can be used. For example, such heavy chain antibody expressing mice can express heavy chain antibodies with any suitable (single) variable domain, such as (single) variable domains from natural sources (e.g. human (single) variable domains, Camelid (single) variable domains or shark (single) variable domains), as well as for example synthetic or semi-synthetic (single) variable domains.

The invention also relates to the V_(HH) sequences or Nanobody sequences that are obtained by the above methods, or alternatively by a method that comprises the one of the above methods and in addition at least the steps of determining the nucleotide sequence or amino acid sequence of said V_(HH) sequence or Nanobody sequence; and of expressing or synthesizing said V_(HH) sequence or Nanobody sequence in a manner known per se, such as by expression in a suitable host cell or host organism or by chemical synthesis.

As mentioned herein, a particularly preferred class of Nanobodies of the invention comprises Nanobodies with an amino acid sequence that corresponds to the amino acid sequence of a naturally occurring V_(HH) domain, but that has been “humanized”, i.e. by replacing one or more amino acid residues in the amino acid sequence of said naturally occurring V_(HH) sequence (and in particular in the framework sequences) by one or more of the amino acid residues that occur at the corresponding position(s) in a V_(H) domain from a conventional 4-chain antibody from a human being (e.g. indicated above). This can be performed in a manner known per se, which will be clear to the skilled person, for example on the basis of the further description herein and the prior art on humanization referred to herein. Again, it should be noted that such humanized Nanobodies of the invention can be obtained in any suitable manner known per se (i.e. as indicated under points (1)-(8) above) and thus are not strictly limited to polypeptides that have been obtained using a polypeptide that comprises a naturally occurring V_(HH) domain as a starting material.

Another particularly preferred class of Nanobodies of the invention comprises Nanobodies with an amino acid sequence that corresponds to the amino acid sequence of a naturally occurring V_(H) domain, but that has been “camelized”, i.e. by replacing one or more amino acid residues in the amino acid sequence of a naturally occurring V_(H) domain from a conventional 4-chain antibody by one or more of the amino acid residues that occur at the corresponding position(s) in a V_(HH) domain of a heavy chain antibody. This can be performed in a manner known per se, which will be clear to the skilled person, for example on the basis of the further description herein. Such “camelizing” substitutions are preferably inserted at amino acid positions that form and/or are present at the V_(H)-V_(L) interface, and/or at the so-called Camelidae hallmark residues, as defined herein (see for example WO 94/04678 and Davies and Riechmann (1994 and 1996), supra). Preferably, the V_(H) sequence that is used as a starting material or starting point for generating or designing the camelized Nanobody is preferably a V_(H) sequence from a mammal, more preferably the V_(H) sequence of a human being, such as a V_(H)3 sequence. However, it should be noted that such camelized Nanobodies of the invention can be obtained in any suitable manner known per se (i.e. as indicated under points (1)-(8) above) and thus are not strictly limited to polypeptides that have been obtained using a polypeptide that comprises a naturally occurring V_(H) domain as a starting material.

For example, again as further described herein, both “humanization” and “camelization” can be performed by providing a nucleotide sequence that encodes a naturally occurring V_(HH) domain or V_(H) domain, respectively, and then changing, in a manner known per se, one or more codons in said nucleotide sequence in such a way that the new nucleotide sequence encodes a “humanized” or “camelized” Nanobody of the invention, respectively. This nucleic acid can then be expressed in a manner known per se, so as to provide the desired Nanobody of the invention. Alternatively, based on the amino acid sequence of a naturally occurring V_(HH) domain or V_(H) domain, respectively, the amino acid sequence of the desired humanized or camelized Nanobody of the invention, respectively, can be designed and then synthesized de novo using techniques for peptide synthesis known per se. Also, based on the amino acid sequence or nucleotide sequence of a naturally occurring V_(HH) domain or V_(H) domain, respectively, a nucleotide sequence encoding the desired humanized or camelized Nanobody of the invention, respectively, can be designed and then synthesized de novo using techniques for nucleic acid synthesis known per se, after which the nucleic acid thus obtained can be expressed in a manner known per se, so as to provide the desired Nanobody of the invention.

Other suitable methods and techniques for obtaining the Nanobodies of the invention and/or nucleic acids encoding the same, starting from naturally occurring V_(H) sequences or preferably V_(HH) sequences, will be clear from the skilled person, and may for example comprise combining one or more parts of one or more naturally occurring V_(H) sequences (such as one or more FR sequences and/or CDR sequences), one or more parts of one or more naturally occurring V_(HH) sequences (such as one or more FR sequences or CDR sequences), and/or one or more synthetic or semi-synthetic sequences, in a suitable manner, so as to provide a Nanobody of the invention or a nucleotide sequence or nucleic acid encoding the same (which may then be suitably expressed). Nucleotide sequences encoding framework sequences of V_(HH) sequences or Nanobodies will be clear to the skilled person based on the disclosure herein and/or the further prior art cited herein (and/or may alternatively be obtained by PCR starting from the nucleotide sequences obtained using the methods described herein) and may be suitably combined with nucleotide sequences that encode the desired CDR's (for example, by PCR assembly using overlapping primers), so as to provide a nucleic acid encoding a Nanobody of the invention.

As mentioned herein, Nanobodies may in particular be characterized by the presence of one or more “Hallmark residues” (as described herein) in one or more of the framework sequences.

Thus, according to one preferred, but non-limiting aspect of the invention, a Nanobody in its broadest sense can be generally defined as a polypeptide comprising:

-   a) an amino acid sequence that is comprised of four framework     regions/sequences interrupted by three complementarity determining     regions/sequences, in which the amino acid residue at position 108     according to the Kabat numbering is Q;     and/or: -   b) an amino acid sequence that is comprised of four framework     regions/sequences interrupted by three complementarity determining     regions/sequences, in which the amino acid residue at position 45     according to the Kabat numbering is a charged amino acid (as defined     herein) or a cysteine residue, and position 44 is preferably an E;     and/or: -   c) an amino acid sequence that is comprised of four framework     regions/sequences interrupted by three complementarity determining     regions/sequences, in which the amino acid residue at position 103     according to the Kabat numbering is chosen from the group consisting     of P, R and S, and is in particular chosen from the group consisting     of R and S.

Thus, in a first preferred, but non-limiting aspect, a Nanobody of the invention may have the structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which

-   a) the amino acid residue at position 108 according to the Kabat     numbering is Q;     and/or in which: -   b) the amino acid residue at position 45 according to the Kabat     numbering is a charged amino acid or a cysteine and the amino acid     residue at position 44 according to the Kabat numbering is     preferably E;     and/or in which: -   c) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of P, R and S, and is     in particular chosen from the group consisting of R and S;     and in which: -   d) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In particular, a Nanobody in its broadest sense can be generally defined as a polypeptide comprising:

-   a) an amino acid sequence that is comprised of four framework     regions/sequences interrupted by three complementarity determining     regions/sequences, in which the amino acid residue at position 108     according to the Kabat numbering is Q;     and/on -   b) an amino acid sequence that is comprised of four framework     regions/sequences interrupted by three complementarity determining     regions/sequences, in which the amino acid residue at position 44     according to the Kabat numbering is E and in which the amino acid     residue at position 45 according to the Kabat numbering is an R;     and/or: -   c) an amino acid sequence that is comprised of four framework     regions/sequences interrupted by three complementarity determining     regions/sequences, in which the amino acid residue at position 103     according to the Kabat numbering is chosen from the group consisting     of P, R and S, and is in particular chosen from the group consisting     of R and S.

Thus, according to a preferred, but non-limiting aspect, a Nanobody of the invention may have the structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which

-   a) the amino acid residue at position 108 according to the Kabat     numbering is Q;     and/or in which: -   b) the amino acid residue at position 44 according to the Kabat     numbering is E and in which the amino acid residue at position 45     according to the Kabat numbering is an R;     and/or in which: -   c) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of P, R and S, and is     in particular chosen from the group consisting of R and S;     and in which: -   d) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In particular, a Nanobody against Targets of the invention according to the invention may have the structure:

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which

-   a) the amino acid residue at position 108 according to the Kabat     numbering is Q;     and/or in which: -   b) the amino acid residue at position 44 according to the Kabat     numbering is E and in which the amino acid residue at position 45     according to the Kabat numbering is an R;     and/or in which: -   c) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of F, R and S, and is     in particular chosen from the group consisting of R and S;     and in which: -   d) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In particular, according to one preferred, but non-limiting aspect of the invention, a Nanobody can generally be defined as a polypeptide comprising an amino acid sequence that is comprised of four framework regions/sequences interrupted by three complementarity determining regions/sequences, in which;

-   a-1) the amino acid residue at position 44 according to the Kabat     numbering is chosen from the group consisting of A, G, E, D, G, Q,     R, S, L; and is preferably chosen from the group consisting of G, E     or Q; and -   a-2) the amino acid residue at position 45 according to the Kabat     numbering is chosen from the group consisting of L, R or C; and is     preferably chosen from the group consisting of L or R; and -   a-3) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of W, R or S; and is     preferably W or R, and is most preferably W; -   a-4) the amino acid residue at position 108 according to the Kabat     numbering is Q;     or in which: -   b-1) the amino acid residue at position 44 according to the Kabat     numbering is chosen from the group consisting of E and Q; and -   b-2) the amino acid residue at position 45 according to the Kabat     numbering is R; and -   b-3) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of W, R and S; and is     preferably W; -   b-4) the amino acid residue at position 108 according to the Kabat     numbering is chosen from the group consisting of Q and L; and is     preferably Q;     or in which: -   c-1) the amino acid residue at position 44 according to the Kabat     numbering is chosen from the group consisting of A, G, E, D, Q, R, S     and L; and is preferably chosen from the group consisting of G, E     and Q; and -   c-2) the amino acid residue at position 45 according to the Kabat     numbering is chosen from the group consisting of L, R and C; and is     preferably chosen from the group consisting of L and R; and -   c-3) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of P, R and S; and is     in particular chosen from the group consisting of R and S; and -   c-4) the amino acid residue at position 108 according to the Kabat     numbering is chosen from the group consisting of Q and L; is     preferably Q;     and in which -   d) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

Thus, in another preferred, but non-limiting aspect, a Nanobody of the invention may have the structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which:

-   a-1) the amino acid residue at position 44 according to the Kabat     numbering is chosen from the group consisting of A, G, E, D, G, Q,     R, S, L; and is preferably chosen from the group consisting of G, E     or Q;     and in which: -   a-2) the amino acid residue at position 45 according to the Kabat     numbering is chosen from the group consisting of L, R or C; and is     preferably chosen from the group consisting of L or R;     and in which: -   a-3) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of W, R or S; and is     preferably W or R, and is most preferably W;     and in which -   a-4) the amino acid residue at position 108 according to the Kabat     numbering is Q;     and in which: -   d) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In another preferred, but non-limiting aspect, a Nanobody of the invention may have the structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which:

-   b-1) the amino acid residue at position 44 according to the Kabat     numbering is chosen from the group consisting of E and Q;     and in which: -   b-2) the amino acid residue at position 45 according to the Kabat     numbering is R;     and in which: -   b-3) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of W, R and S; and is     preferably W;     and in which: -   b-4) the amino acid residue at position 108 according to the Kabat     numbering is chosen from the group consisting of Q and L; and is     preferably Q;     and in which: -   d) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In another preferred, but non-limiting aspect, a Nanobody of the invention may have the structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which:

-   c-1) the amino acid residue at position 44 according to the Kabat     numbering is chosen from the group consisting of A, G, E, D, Q, R, S     and L; and is preferably chosen from the group consisting of G, E     and Q;     and in which: -   c-2) the amino acid residue at position 45 according to the Kabat     numbering is chosen from the group consisting of L, R and C; and is     preferably chosen from the group consisting of L and R;     and in which: -   c-3) the amino acid residue at position 103 according to the Kabat     numbering is chosen from the group consisting of P, R and S; and is     in particular chosen from the group consisting of R and S;     and in which: -   c-4) the amino acid residue at position 108 according to the Kabat     numbering is chosen from the group consisting of Q and L; is     preferably Q;     and in which: -   d) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

Two particularly preferred, but non-limiting groups of the Nanobodies of the invention are those according to a) above; according to (a-1) to (a-4) above; according to b) above; according to (b-1) to (b-4) above; according to (c) above; and/or according to (c-1) to (c-4) above, in which either:

-   i) the amino acid residues at positions 44-47 according to the Kabat     numbering form the sequence GLEW (or a GLEW-like sequence as     described herein) and the amino acid residue at position 108 is Q;     or in which: -   ii) the amino acid residues at positions 43-46 according to the     Kabat numbering form the sequence KERE or KQRE (or a KERE-like     sequence as described) and the amino acid residue at position 108 is     Q or L, and is preferably Q.

Thus, in another preferred, but non-limiting aspect, a Nanobody of the invention may have the structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which:

-   i) the amino acid residues at positions 44-47 according to the Kabat     numbering form the sequence GLEW (or a GLEW-like sequence as defined     herein) and the amino acid residue at position 108 is Q;     and in which: -   ii) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In another preferred, but non-limiting aspect, a Nanobody of the invention may have the structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which:

-   i) the amino acid residues at positions 43-46 according to the Kabat     numbering form the sequence KERE or KQRE (or a KERE-like sequence)     and the amino acid residue at position 108 is Q or L, and is     preferably Q;     and in which: -   ii) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In the Nanobodies of the invention in which the amino acid residues at positions 43-46 according to the Kabat numbering form the sequence KERE or KQRE, the amino acid residue at position 37 is most preferably F. In the Nanobodies of the invention in which the amino acid residues at positions 44-47 according to the Kabat numbering form the sequence GLEW, the amino acid residue at position 37 is chosen from the group consisting of Y, H, I, L, V or F, and is most preferably V.

Thus, without being limited hereto in any way, on the basis of the amino acid residues present on the positions mentioned above, the Nanobodies of the invention can generally be classified on the basis of the following three groups:

-   i) The “GLEW-group”: Nanobodies with the amino acid sequence GLEW at     positions 44-47 according to the Kabat numbering and Q at position     108 according to the Kabat numbering. As further described herein,     Nanobodies within this group usually have a V at position 37, and     can have a W, P, R or S at position 103, and preferably have a W at     position 103. The CLEW group also comprises some GLEW-like sequences     such as those mentioned in Table A-3 below. More generally, and     without limitation, Nanobodies belonging to the CLEW-group can be     defined as Nanobodies with a G at position 44 and/or with a W at     position 47, in which position 46 is usually E and in which     preferably position 45 is not a charged amino acid residue and not     cysteine; -   ii) The “KERE-group”: Nanobodies with the amino acid sequence KERE     or KQRE (or another KERE-like sequence) at positions 43-46 according     to the Kabat numbering and Q or L at position 108 according to the     Kabat numbering. As further described herein, Nanobodies within this     group usually have a F at position 37, an L or F at position 47; and     can have a W, P, R or S at position 103, and preferably have a W at     position 103. More generally, and without limitation, Nanobodies     belonging to the KERE-group can be defined as Nanobodies with a K, Q     or R at position 44 (usually K) in which position 45 is a charged     amino acid residue or cysteine, and position 47 is as further     defined herein; -   iii) The “103 P, R, S-group”: Nanobodies with a P, R or S at     position 103. These Nanobodies can have either the amino acid     sequence GLEW at positions 44-47 according to the Kabat numbering or     the amino acid sequence KERE or KQRE at positions 43-46 according to     the Kabat numbering, the latter most preferably in combination with     an F at position 37 and an L or an F at position 47 (as defined for     the KERE-group); and can have Q or L at position 108 according to     the Kabat numbering, and preferably have Q.

Also, where appropriate, Nanobodies may belong to (i.e. have characteristics of) two or more of these classes. For example, one specifically preferred group of Nanobodies has GLEW or a GLEW-like sequence at positions 44-47; P, R or S (and in particular R) at position 103; and Q at position 108 (which may be humanized to L).

More generally, it should be noted that the definitions referred to above describe and apply to Nanobodies in the form of a native (i.e. non-humanized) V_(HH) sequence, and that humanized variants of these Nanobodies may contain other amino acid residues than those indicated above (i.e. one or more humanizing substitutions as defined herein). For example, and without limitation, in some humanized Nanobodies of the GLEW-group or the 103 P, R, S-group, Q at position 108 may be humanized to 108L. As already mentioned herein, other humanizing substitutions (and suitable combinations thereof) will become clear to the skilled person based on the disclosure herein. In addition, or alternatively, other potentially useful humanizing substitutions can be ascertained by comparing the sequence of the framework regions of a naturally occurring V_(H) sequence with the corresponding framework sequence of one or more closely related human V_(H) sequences, after which one or more of the potentially useful humanizing substitutions (or combinations thereof) thus determined can be introduced into said V_(HH) sequence (in any manner known per se, as further described herein) and the resulting humanized V_(HH) sequences can be tested for affinity for the target, for stability, for ease and level of expression, and/or for other desired properties. In this way, by means of a limited degree of trial and error, other suitable humanizing substitutions (or suitable combinations thereof) can be determined by the skilled person based on the disclosure herein. Also, based on the foregoing, (the framework regions of) a Nanobody may be partially humanized or fully humanized.

Thus, in another preferred, but non-limiting aspect, a Nanobody of the invention may be a Nanobody belonging to the GLEW-group (as defined herein), and in which CDR1, CDR2 and CDR3 are as defined herein, and are preferably as defined according to one of the preferred aspects herein, and are more preferably as defined according to one of the more preferred aspects herein.

In another preferred, but non-limiting aspect, a Nanobody of the invention may be a Nanobody belonging to the KERE-group (as defined herein), and CDR1, CDR2 and CDR3 are as defined herein, and are preferably as defined according to one of the preferred aspects herein, and are more preferably as defined according to one of the more preferred aspects herein.

Thus, in another preferred, but non-limiting aspect, a Nanobody of the invention may be a Nanobody belonging to the 103 P, R, S-group (as defined herein), and in which CDR1, CDR2 and CDR3 are as defined herein, and are preferably as defined according to one of the preferred aspects herein, and are more preferably as defined according to one of the more preferred aspects herein.

Also, more generally and in addition to the 108Q, 43E/44R and 103 P,R,S residues mentioned above, the Nanobodies of the invention can contain, at one or more positions that in a conventional V_(H) domain would form (part of) the V_(H)/V_(L) interface, one or more amino acid residues that are more highly charged than the amino acid residues that naturally occur at the same position(s) in the corresponding naturally occurring V_(H) sequence, and in particular one or more charged amino acid residues (as mentioned in Table A-2). Such substitutions include, but are not limited to, the GLEW-like sequences mentioned in Table A-3 below; as well as the substitutions that are described in the International Application WO 00/29004 for so-called “microbodies”, e.g. so as to obtain a Nanobody with Q at position 108 in combination with KLEW at positions 44-47. Other possible substitutions at these positions will be clear to the skilled person based upon the disclosure herein.

In one aspect of the Nanobodies of the invention, the amino acid residue at position 83 is chosen from the group consisting of L, M, S, V and W; and is preferably L.

Also, in one aspect of the Nanobodies of the invention, the amino acid residue at position 83 is chosen from the group consisting of R, K, N, E, G, I, T and Q; and is most preferably either K or E (for Nanobodies corresponding to naturally occurring V_(HH) domains) or R (for “humanized” Nanobodies, as described herein). The amino acid residue at position 84 is chosen from the group consisting of P, A, R, S, D T, and V in one aspect, and is most preferably P (for Nanobodies corresponding to naturally occurring V_(HH) domains) or R (for “humanized” Nanobodies, as described herein).

Furthermore, in one aspect of the Nanobodies of the invention, the amino acid residue at position 104 is chosen from the group consisting of G and D; and is most preferably G.

Collectively, the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108, which in the Nanobodies are as mentioned above, will also be referred to herein as the “Hallmark Residues”. The Hallmark Residues and the amino acid residues at the corresponding positions of the most closely related human V_(H) domain, V_(H)3, are summarized in Table A-3.

Some especially preferred but non-limiting combinations of these Hallmark Residues as occur in naturally occurring V_(HH) domains are mentioned in Table A-4. For comparison, the corresponding amino acid residues of the human V_(H)3 called DP-47 have been indicated in italics.

TABLE A-3 Hallmark Residues in Nanobodies Position Human V_(H)3 Hallmark Residues 11 L, V; L, M, S, V, W; preferably L predominantly L 37 V, I, F; usually V F⁽¹⁾, Y, H, I, L or V, preferably F⁽¹⁾ or Y  44⁽⁸⁾ G G⁽²⁾, E⁽³⁾, A, D, Q, R, S, L; preferably G⁽²⁾, E⁽³⁾ or Q; most preferably G⁽²⁾ or E⁽³⁾  45⁽⁸⁾ L L⁽²⁾, R⁽³⁾, C, I, L, P, Q, V; preferably L⁽²⁾ or R⁽³⁾  47⁽⁸⁾ W, Y W⁽²⁾, L⁽¹⁾ or F⁽¹⁾, A, G, I, M, R, S, V or Y; preferably W⁽²⁾, L⁽¹⁾, F⁽¹⁾ or R 83 R or K; usually R R, K⁽⁵⁾, N, E⁽⁵⁾, G, I, M, Q or T; preferably K or R; most preferably K 84 A, T, D; P⁽⁵⁾, A, L, R, S, T, D, V; preferably P predominantly A 103  W W⁽⁴⁾, P⁽⁶⁾, R⁽⁶⁾, S; preferably W 104  G G or D; preferably G 108  L, M or T; Q, L⁽⁷⁾ or R; preferably Q or L⁽⁷⁾ predominantly L Notes: ⁽¹⁾In particular, but not exclusively, in combination with KERE or KQRE at positions 43-46. ⁽²⁾Usually as GLEW at positions 44-47. ⁽³⁾Usually as KERE or KQRE at positions 43-46, e.g. as KEREL, KEREF, KQREL, KQREF or KEREG at positions 43-47. Alternatively, also sequences such as TERE (for example TEREL), KECE (for example KECEL or KECER), RERE (for example REREG), QERE (for example QEREG), KGRE (for example KGREG), KDRE (for example KDREV) are possible. Some other possible, but less preferred sequences include for example DECKL and NVCEL. ⁽⁴⁾With both GLEW at positions 44-47 and KERE or KQRE at positions 43-46. ⁽⁵⁾Often as KP or EP at positions 83-84 of naturally occurring V_(HH) domains. ⁽⁶⁾In particular, but not exclusively, in combination with GLEW at positions 44-47. ⁽⁷⁾With the proviso that when positions 44-47 are GLEW, position 108 is always Q in (non-humanized) V_(HH) sequences that also contain a W at 103. ⁽⁸⁾The GLEW group also contains GLEW-like sequences at positions 44-47, such as for example GVEW, EPEW, GLER, DQEW, DLEW, GIEW, ELEW, GPEW, EWLP, GPER, GLER and ELEW.

TABLE A-4 Some preferred but non-limiting combinations of Hallmark Residues in naturally occurring Nanobodies. 11 37 44 45 47 83 84 103 104 108 DP-47 (human) M V G L W R A W G L “KERE” group L F E R L K P W G Q L F E R F E P W G Q L F E R F K P W G Q L Y Q R L K P W G Q L F L R V K P Q G Q L F Q R L K P W G Q L F E R F K P W G Q “GLEW” group L V G L W K S W G Q M V G L W K P R G Q For humanization of these combinations, reference is made to the specification.

In the Nanobodies, each amino acid residue at any other position than the Hallmark Residues can be any amino acid residue that naturally occurs at the corresponding position (according to the Kabat numbering) of a naturally occurring V_(HH) domain.

Such amino acid residues will be clear to the skilled person. Tables A-5 to A-8 mention some non-limiting residues that can be present at each position (according to the Kabat numbering) of the FR1, FR2, FR3 and FR4 of naturally occurring V_(HH) domains. For each position, the amino acid residue that most frequently occurs at each position of a naturally occurring V_(HH) domain (and which is the most preferred amino acid residue for said position in a Nanobody) is indicated in bold; and other preferred amino acid residues for each position have been underlined (note: the number of amino acid residues that are found at positions 26-30 of naturally occurring V_(HH) domains supports the hypothesis underlying the numbering by Chothia (supra) that the residues at these positions already form part of CDR1).

In Tables A-5-A-8, some of the non-limiting residues that can be present at each position of a human V_(H)3 domain have also been mentioned. Again, for each position, the amino acid residue that most frequently occurs at each position of a naturally occurring human V_(H)3 domain is indicated in bold; and other preferred amino acid residues have been underlined.

For reference only, Tables A-5-A-8 also contain data on the V_(HH) entropy (“V_(HH) Ent.”) and V_(HH) variability (“V_(HH) Var.”) at each amino acid position for a representative sample of 1118 V_(HH) sequences (data kindly provided by David Lutje Hulling and Prof. Theo Verrips of Utrecht University). The values for the V_(HH) entropy and the V_(HH) variability provide a measure for the variability and degree of conservation of amino acid residues between the 1118 V_(HH) sequences analyzed: low values (i.e. <1, such as <0.5) indicate that an amino acid residue is highly conserved between the V_(HH) sequences (i.e. little variability). For example, the G at position 8 and the G at position 9 have values for the V_(HH) entropy of 0.1 and 0 respectively, indicating that these residues are highly conserved and have little variability (and in case of position 9 is G in all 1118 sequences analysed), whereas for residues that faint part of the CDR's generally values of 1.5 or more are found (data not shown). Note that (1) the amino acid residues listed in the second column of Tables A-5-A-8 are based on a bigger sample than the 1118 V_(HH) sequences that were analysed for determining the V_(HH) entropy and V_(HH) variability referred to in the last two columns; and (2) the data represented below support the hypothesis that the amino acid residues at positions 27-30 and maybe even also at positions 93 and 94 already form part of the CDR's (although the invention is not limited to any specific hypothesis or explanation, and as mentioned above, herein the numbering according to Kabat is used). For a general explanation of sequence entropy, sequence variability and the methodology for determining the same, see Oliveira et al., PROTEINS: Structure, Function and Genetics, 52: 544-552 (2003).

TABLE A-5 Non-limiting examples of amino acid residues in FR1 (for the footnotes, see the footnotes to Table A-3) Amino acid residue(s): V_(HH) V_(HH) Pos. Human V_(H)3 Camelid V_(HH)'s Ent. Var. 1 E, Q Q, A, E — — 2 V V 0.2 1 3 Q Q, K 0.3 2 4 L L 0.1 1 5 V, L Q, E, L, V 0.8 3 6 E E, D, Q, A 0.8 4 7 S, T S, F 0.3 2 8 G, R G 0.1 1 9 G G 0 1 10 G, V G, D, R 0.3 2 11 Hallmark residue: L, M, S, V, W; preferably L 0.8 2 12 V, I V, A 0.2 2 13 Q, K, R Q, E, K, P, R 0.4 4 14 P A, Q, A, G, P, S, T, V 1 5 15 G G 0 1 16 G, R G, A, E, D 0.4 3 17 S S, F 0.5 2 18 L L, V 0.1 1 19 R, K R, K, L, N, S, T 0.6 4 20 L L, F, I, V 0.5 4 21 S S, A, F, T 0.2 3 22 C C 0 1 23 A, T A, D, E, P, S, T, V 1.3 5 24 A A, I, L, S, T, V 1 6 25 S S, A, F, P, T 0.5 5 26 G G, A, D, E, R, S, T, V 0.7 7 27 F S, F, R, L, P, G, N, 2.3 13 28 T N, T, E, D, S, I, R, A, G, R, F, Y 1.7 11 29 F, V F, L, D, S, I, G, V, A 1.9 11 30 S, D, G N, S, E, G, A, D, M, T 1.8 11

TABLE A-6 Non-limiting examples of amino acid residues in FR2 (for the footnotes, see the footnotes to Table A-3) Amino acid residue(s): V_(HH) V_(HH) Pos. Human V_(H)3 Camelid V_(HH)'s Ent. Var. 36 W W 0.1 1 37 Hallmark residue: F⁽¹⁾, H, I, L, Y 1.1 6 or V, preferably F⁽¹⁾ or Y 38 R R 0.2 1 39 Q Q, H, P, R 0.3 2 40 A A, F, G, L, P, T, V 0.9 7 41 P, S, T P, A, L, S 0.4 3 42 G G, E 0.2 2 43 K K, D, E, N, Q, R, T, V 0.7 6 44 Hallmark residue: G⁽²⁾, E⁽³⁾, A, D, Q, 1.3 5 R, S, L; preferably G⁽²⁾, E⁽³⁾ or Q; most preferably G⁽²⁾ or E⁽³⁾. 45 Hallmark residue: L⁽²⁾, R⁽³⁾, C, I, L, P, Q, V; 0.6 4 preferably L⁽²⁾ or R⁽³⁾ 46 E, V E, D, K, Q, V 0.4 2 47 Hallmark residue: W⁽²⁾, L⁽¹⁾ or F⁽¹⁾, A, G, I, 1.9 9 M, R, S, V or Y; preferably W⁽²⁾, L⁽¹⁾, F⁽¹⁾ or R 48 V V, I, L 0.4 3 49 S, A, G A, S, G, T, V 0.8 3

TABLE A-7 Non-limiting examples of amino acid residues in FR3 (for the footnotes, see the footnotes to Table A-3) Amino acid residue(s): V_(HH) V_(HH) Pos. Human V_(H)3 Camelid V_(HH)'s Ent. Var. 66 R R 0.1 1 67 F F, L, V 0.1 1 68 T T, A, N, S 0.5 4 69 I I, L, M, V 0.4 4 70 S S, A, F, T 0.3 4 71 R R, G, H, I, L, K, Q, S, T, W 1.2 8 72 D, E D, E, G, N, V 0.5 4 73 N, D, G N, A, D, F, I, K, L, R, S, T, V, Y 1.2 9 74 A, S A, D, G, N, P, S, T, V 1 7 75 K K, A, E, K, L, N, Q, R 0.9 6 76 N, S N, D, K, R, S, T, Y 0.9 6 77 S, T, I T, A, E, I, M, P, S 0.8 5 78 L, A V, L, A, F, G, I, M 1.2 5 79 Y, H Y, A, D, F, H, N, S, T 1 7 80 L L, F, V 0.1 1 81 Q Q, E, I, L, R, T 0.6 5 82 M M, I, L, V 0.2 2  82a N, G N, D, G, H, S, T 0.8 4  82b S S, N, D, G, R, T 1 6  82c L L, P, V 0.1 2 83 Hallmark residue: R, K⁽⁵⁾, N, E⁽⁵⁾, G, I, M, Q or T; 0.9 7 preferably K or R; most preferably K 84 Hallmark residue: P⁽⁵⁾, A, D, L, R, S, T, V; 0.7 6 preferably P 85 E, G E, D, G, Q 0.5 3 86 D D 0 1 87 T, M T, A, S 0.2 3 88 A A, G, S 0.3 2 89 V, L V, A, D, I, L, M, N, R, T 1.4 6 90 Y Y, F 0 1 91 Y, H Y, D, F, H, L, S, T, V 0.6 4 92 C C 0 1 93 A, K, T A, N, G, H, K, N, R, S, T, V, Y 1.4 10 94 K, R, T A, V, C, F, G, I, K, L, R, S or T 1.6 9

TABLE A-8 Non-limiting examples of amino acid residues in FR4 (for the footnotes, see the footnotes to Table A-3) Amino acid residue(s): V_(HH) V_(HH) Pos. Human V_(H)3 Camelid V_(HH)'s Ent. Var. 103 Hallmark residue: W⁽⁴⁾, P⁽⁶⁾, R⁽⁶⁾, S; preferably W 0.4 2 104 Hallmark residue: G or D; preferably G 0.1 1 105 Q, R Q, E, K, P, R 0.6 4 106 G G 0.1 1 107 T T, A, I 0.3 2 108 Hallmark residue: Q, L⁽⁷⁾ or R: preferably Q or L⁽⁷⁾ 0.4 3 109 V V 0.1 1 110 T T, I, A 0.2 1 111 V V, A, I 0.3 2 112 S S, F 0.3 1 113 S S, A, L, P, T 0.4 3

Thus, in another preferred, but not limiting aspect, a Nanobody of the invention can be defined as an amino acid sequence with the (general) structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which:

-   i) one or more of the amino acid residues at positions 11, 37, 44,     45, 47, 83, 84, 103, 104 and 108 according to the Kabat numbering     are chosen from the Hallmark residues mentioned in Table A-3;     and in which: -   ii) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

The above Nanobodies may for example be V_(HH) sequences or may be humanized Nanobodies. When the above Nanobody sequences are V_(HH) sequences, they may be suitably humanized, as further described herein. When the Nanobodies are partially humanized Nanobodies, they may optionally be further suitably humanized, again as described herein.

In particular, a Nanobody of the invention can be an amino acid sequence with the (general) structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which:

-   i) (preferably) one or more of the amino acid residues at positions     11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to the Kabat     numbering are chosen from the Hallmark residues mentioned in Table     A-3 (it being understood that V_(HH) sequences will contain one or     more Hallmark residues; and that partially humanized Nanobodies will     usually, and preferably, [still] contain one or more Hallmark     residues [although it is also within the scope of the invention to     provide—where suitable in accordance with the invention—partially     humanized Nanobodies in which all Hallmark residues, but not one or     more of the other amino acid residues, have been humanized]; and     that in fully humanized Nanobodies, where suitable in accordance     with the invention, all amino acid residues at the positions of the     Hallmark residues will be amino acid residues that occur in a human     V_(H)3 sequence. As will be clear to the skilled person based on the     disclosure herein that such V_(HH) sequences, such partially     humanized Nanobodies with at least one Hallmark residue, such     partially humanized Nanobodies without Hallmark residues and such     fully humanized Nanobodies all form aspects of this invention);     and in which: -   ii) said amino acid sequence has at least 80% amino acid identity     with at least one of the amino acid sequences of SEQ ID NO's: 1 to     22, in which for the purposes of determining the degree of amino     acid identity, the amino acid residues that form the CDR sequences     (indicated with X in the sequences of SEQ ID NO's: 1 to 22) are     disregarded;     and in which: -   iii) CDR1, CDR2 and CDR3 are as defined herein, and are preferably     as defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

The above Nanobodies may for example be V_(HH) sequences or may be humanized Nanobodies. When the above Nanobody sequences are V_(HH) sequences, they may be suitably humanized, as further described herein. When the Nanobodies are partially humanized Nanobodies, they may optionally be further suitably humanized, again as described herein.

TABLE A-9 Representative amino acid sequences for Nanobodies of the KERE, GLEW and P, R, S 103 group. The CDR's are indicated with XXXX KERE sequence no. 1 SEQ ID NO: 1 EVQLVESGGGLVQPGGSLRLSCAASGIPFSXXXXXWFRQAPGKQRDSVAXXXXXRFTI SRDNAKNTVYLQMNSLKPEDTAVYRCYFXXXXXWGQGTQVTVSS KERE sequence no. 2 SEQ ID NO: 2 QVKLEESGGGLVQAGGSLRLSCVGSGRTFSXXXXXWFRLAPGKEREEVAXXXXXRETI SRDTASNRGYLFIMNNLTPEDTAVYYCAAXXXXXWGQGTQVIVSS KERE sequence no. 3 SEQ ID NO: 3 AVQLVDSGGGLVQAGDSLKLSCALTGGAFTXXXXXWFRQTPGREREFVAXXXXXRFTI SRDNAKNMVYLRMNSLIPEDAAVYSCAAXXXXXWGQGTLVTVSS KERE sequence no. 4 SEQ ID NO: 4 QVQLVESGGGLVEAGGSLRLSCTASESPFRXXXXXWFRQTSGQEREFVAXXXXXRFTI SRDDAKNTVWLHGSTLKPEDTAVYYCAAXXXXXWGQGTQVTVSS KERE sequence no. 5 SEQ ID NO: 5 AVQLVESGGGLVQGGGSLRLACAASERIFDXXXXXWYRQGPGNERELVAXXXXXRFTI SMDYTKQTVYLFIMNSLRPEDTGLYYCKIXXXXXWGQGTQVTVSS KERE sequence no. 6 SEQ ID NO: 6 DVKEVESGGGLVQAGGSLRLSCVASGENFDXXXXXWERQAPGKEREEVAXXXXXRFTI SSEKDKNSVYLQMNSLKPEDTALYICAGXXXXXWGRGTQVTVSS KERE sequence no. 7 SEQ ID NO: 7 QVRLAESGGGLVQSGGSLRLSCVASGSTYTXXXXXWYRQYPGKQRALVAXXXXXRFTI ARDSTKDTFCLQMNNLKPEDTAVYYCYAXXXXXWGQGTQVIVSS KERE sequence no. 8 SEQ ID NO: 8 EVQLVESGGGLVQAGGSLRLSCAASGFTSDXXXXXVVFRQAPGKPREGVSXXXXXRFT ISTDNAKNWHLLMNRVNAEDTALYYCAVXXXXXWGRGTRVTVSS KERE sequence no. 9 SEQ ID NO: 9 QVQLVESGGGLVOPGGSLRLSCQASGDISTXXXXXWYROVPGKLREFVAXXXXXRFTI SGDNAKRAIYLQMNINLKPDDTAVYYCNRXXXXXVVGQGTQVTVSP KERE sequence no. 10 SEQ ID NO: 10 QVPVVESGGGLVQAGDSLRLFCAVPSFTSTXXXXXWFRQAPGKEREFVAXXXXXRFTI SRNATKNTLTLRMDSLKPEDTAVYYCAAXXXXXWGQGTQVTVSS KERE sequence no. 11 SEQ ID NO: 11 EVQLVESGGGLVQAGDSLRLFCTVSGGTASXXXXXWFRQAPGEKREFVAXXXXXRFTI ARENAGNMVYLQMNNLKPDDTALYTCAAXXXXXWGRGTQVIVSS KERE sequence no. 12 SEQ ID NO: 12 AVQLVESGGDSVQPGDSQTLSCAASGRTNSXXXXXWFRQAPGKERVFLAXXXXXRFTI SRDSAKNMMYLQMNNLKPQDTAVYYCAAXXXXXWGQGTQVTVSS KERE sequence no 13 SEQ ID NO: 13 AVQLVESGGGLVQAGGSLRLSCVVSGLTSSXXXXXWFRQTPWQERDFVAXXXXXRFTI SRDNYKDTVLLEMNFLKPEDTAIYYCAAXXXXXWGQGTOVTVSS KERE sequence no. 14 SEQ ID NO: 14 AVQLVESGGGLVQAGASLRLSCATSTRTLDXXXXXWFRQAPGRDREFVAXXXXXRFTV SRDSAENTVALQMNSLKPEDTAVYYCAAXXXXXVVGQGTRVTVSS KERE sequence no. 15 SEQ ID NO: 15 QVQLVESGGGLVQPGGSLRLSCTVSRLTAHXXXXXWFRQAPGKEREAVSXXXXXRFTI SRDYAGNTAFLOMDSLKPEDTGVYYCATXXXXXWGQGTQVTVSS KERE sequence no. 16 SEQ ID NO: 16 EVOLVESGGELVQAGGSLKLSCTASGRNEVXXXXXWERRAPGKEREFVAXXXXXRFTV SRDNGKNTAYLRMNSLKPEDTADYYCAVXXXXXLGSGTQVTVSS GLEW sequence no. 1 SEQ ID NO: 17 AVQLVESGGGLVQPGGSLRLSCAASGFTFSXXXXXWVRQAPGKVLEWVSXXXXXRFTI SRDNAKNTLYLQMNSLKPEDTAVYYCVKXXXXXGSQGTQVTVSS GLEW sequence no. 2 SEQ ID NO: 18 EVQLVESGGGLVQPGGSLRLSCVCVSSGCTXXXXXWVRQAPGKAEEWVSXXXXXRFKI SRDNAKKTLYLQMNSLGPEDTAMYYCQRXXXXXRGQGTQVTVSS GLEW sequence no. 3 SEQ ID NO: 19 EVQLVESGGGLALPGGSLTLSCVFSGSTFSXXXXXWVRHTPGKAEEWVSXXXXXRFTI SRDNAKNTLYLEMNSLSPEDTAMYYCGRXXXXXRSKGIQVTVSS P, R, S 103 sequence no. 1 SEQ ID NO: 20 AVOLVESGGGLVQAGGSLRLSCAASGRTESXXXXXWERQAPGKEREFVAXXXXXRFTI SRDNAKNTVYLQMNSLKPEDTAVYYCAAXXXXXRGQGTQVTVSS P, R, S 103 sequence no. 2 SEQ ID NO: 21 DVQLVESGGDLVQPGGSLRLSCAASGFSFDXXXXXWLRQTPGKGLEWVGXXXXXRFTI SRDNAKNMLYLHLNNLKSEDTAVYYCRRXXXXXLGQGTQVIVSS P, R, S 103 sequence no. 3 SEQ ID NO: 22 EVQLVESGGGLVQPGGSLRLSCVCVSSGCTXXXXXWVRQAPGKAEEWVSXXXXXRFKI SRDNAKKTLYLQMNSLGPEDTAMYYCQRXXXXXRGQGTQVTVSS

In particular, a Nanobody of the invention of the KERE group can be an amino acid sequence with the (general) structure

FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4

in which:

-   i) the amino acid residue at position 45 according to the Kabat     numbering is a charged amino acid (as defined herein) or a cysteine     residue, and position 44 is preferably an E;     and in which: -   ii) FR1 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-10 Representative FW1 sequences for Nanobodies of the KERE-group. KERE FW1 sequence no. 1 SEQ ID NO: 23 QVQRVESGGGLVQAGGSLRLSCAASGRTSS KERE FW1 sequence no. 2 SEQ ID NO: 24 QVQLVESGGGLVQTGDSLSLSCSASGRTFS KERE FW1 sequence no. 3 SEQ ID NO: 25 QVKLEESGGGLVQAGDSLRLSCAATGRAFG KERE FW1 sequence no. 4 SEQ ID NO: 26 AVQLVESGGGLVQPGESLGLSCVASGRDFV KERE FW1 sequence no. 5 SEQ ID NO: 27 EVQLVESGGGLVQAGGSLRLSCEVLGRTAG KERE FW1 sequence no. 6 SEQ ID NO: 28 QVQLVESGGGWVQPGGSLRLSCAASETILS KERE FW1 sequence no. 7 SEQ ID NO: 29 QVQLVESGGGTVQPGGSLNLSCVASGNTFN KERE FW1 sequence no. 8 SEQ ID NO: 30 EVQLVESGGGLAQPGGSLQLSCSAPGFTLD KERE FW1 sequence no. 9 SEQ ID NO: 31 AQELEESGGGLVQAGGSLRLSCAASGRTFN and in which:

-   iii) FR2 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-11 Representative FW2 sequences for Nanobodies of the KERE-group. KERE FW2 sequence no. 1 SEQ ID NO: 41 WERQAPGKEREEVA KERE FW2 sequence no. 2 SEQ ID NO: 42 WFRQTPGREREFVA KERE FW2 sequence no. 3 SEQ ID NO: 43 WYRQAPGKQREMVA KERE FW2 sequence no. 4 SEQ ID NO: 44 WYRQGPGKQRELVA KERE FW2 sequence no. 5 SEQ ID NO: 45 WIRQAPGKEREGVS KERE FW2 sequence no. 6 SEQ 1D NO: 46 WFREAPGKEREGIS KERE FW2 sequence no. 7 SEQ ID N0: 47 WYRQAPGKERDLVA KERE FW2 sequence no. 8 SEQ ID NO: 48 WFRQAPGKQREEVS KERE FW2 sequence no. 9 SEQ ID NO: 49 WFRQPPGKVREFVG and in which:

-   iv) FR3 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-12 Representative FW3 sequences for Nanobodies of the KERE-group. KERE FW3 sequence no. 1  SEQ ID NO: 50 RFTISRDNAKNTVYLQMNSLKPEDTAVYRCYF KERE FW3 sequence no. 2  SEQ ID NO: 51 RFAISRDNNKNTGYLOMNSLEPEDTAVYYCAA KERE FW3 sequence no. 3  SEQ ID NO: 52 RFTVARNNAKNTVNLEMNSLKPEDTAVYYCAA KERE FW3 sequence no. 4  SEQ ID NO: 53 RFTISRDIAKNTVDLLMNNLEPEDTAVYYCAA KERE FW3 sequence no. 5  SEQ ID NO: 54 RLTISRDNAVDTMYLQMNSLKPEDTAVYYCAA KERE FW3 sequence no. 6  SEQ ID NO: 55 RFTISRDNAKNTVYLQMDNVKPEDTAIYYCAA KERE FW3 sequence no. 7  SEQ ID NO: 56 RFTISKDSGKNTVYLQMTSLKPEDTAVYYCAT KERE FW3 sequence no. 8  SEQ ID NO: 57 RFTISRDSAKNMMYLQMNNLKPQDTAVYYCAA KERE FW3 sequence no. 9  SEQ ID NO: 58 RFTISRENDKSTVYLQLNSLKPEDTAVYYCAA KERE FW3 sequence no. 10 SEQ ID NO: 59 RFTISRDYAGNTAYLQMNSLKPEDTGVYYCAT and in which:

-   v) FR4 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-13 Representative FW4 sequences for Nanobodies of the KERE-group. KERE FW4 sequence no. 1 SEQ ID NO: 60 WGQGTQVTVSS KERE FW4 sequence no. 2 SEQ ID NO: 61 WGKGTLVTVSS KERE FW4 sequence no. 3 SEQ ID NO: 62 RGQGTRVTVSS KERE FW4 sequence no. 4 SEQ ID NO: 63 WGLGTQVTISS and in which:

-   vi) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In the above Nanobodies, one or more of the further Hallmark residues are preferably as described herein (for example, when they are V_(HH) sequences or partially humanized Nanobodies).

Also, the above Nanobodies may for example be V_(HH) sequences or may be humanized Nanobodies. When the above Nanobody sequences are V_(HH) sequences, they may be suitably humanized, as further described herein. When the Nanobodies are partially humanized Nanobodies, they may optionally be further suitably humanized, again as described herein.

With regard to framework 1, it will be clear to the skilled person that, when an amino acid sequence as outlined above is generated by expression of a nucleotide sequence, the first four amino acid sequences (i.e. amino acid residues 1-4 according to the Kabat numbering) may often be determined by the primer(s) that have been used to generate said nucleic acid. Thus, for determining the degree of amino acid identity, the first four amino acid residues are preferably disregarded.

Also, with regard to framework 1, and although amino acid positions 27 to 30 are according to the Kabat numbering considered to be part of the framework regions (and not the CDR's), it has been found by analysis of a database of more than 1000 V_(HH) sequences that the positions 27 to 30 have a variability (expressed in terms of V_(HH) entropy and V_(HH) variability—see Tables A-5 to A-8) that is much greater than the variability on positions 1 to 26. Because of this, for determining the degree of amino acid identity, the amino acid residues at positions 27 to 30 are preferably also disregarded.

In view of this, a Nanobody of the KERE class may be an amino acid sequence that is comprised of four framework regions/sequences interrupted by three complementarity determining regions/sequences, in which:

-   i) the amino acid residue at position 45 according to the Kabat     numbering is a charged amino acid (as defined herein) or a cysteine     residue, and position 44 is preferably an E;     and in which: -   ii) FR1 is an amino acid sequence that, on positions 5 to 26 of the     Kabat numbering, has at least 80% amino acid identity with at least     one of the following amino acid sequences:

TABLE A-14 Representative FW1 sequences (amino acid residues 5 to 26) for Nanobodies of the KERE-group. KERE FW1 sequence no. 10 SEQ ID NO: 32 VESGGGLVQPGGSLRLSCAASG KERE FW1 sequence no. 11 SEQ ID NO: 33 VDSGGGLVQAGDSLKLSCALTG KERE FW1 sequence no. 12 SEQ ID NO: 34 VDSGGGLVQAGDSLRLSCAASG KERE FW1 sequence no. 13 SEQ ID NO: 35 VDSGGGLVEAGGSLRLSCQVSE KERE FW1 sequence no. 14 SEQ ID NO: 36 QDSGGGSVQAGGSLKLSCAASG KERE FW1 sequence no. 15 SEQ ID NO: 37 VQSGGRLVQAGDSLRLSCAASE KERE FW1 sequence no. 16 SEQ ID NO: 38 VESGGTLVQSGDSLKLSCASST KERE FW1 sequence no. 17 SEQ ID NO: 39 MESGGDSVQSGGSLTLSCVASG KERE FW1 sequence no. 18 SEQ ID NO: 40 QASGGGLVQAGGSLRLSCSASV and in which:

-   iii) FR2, FR3 and FR4 are as mentioned herein for FR2, FR3 and FR4     of Nanobodies of the KERE-class;     and in which: -   iv) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

The above Nanobodies may for example be V_(HH) sequences or may be humanized Nanobodies. When the above Nanobody sequences are V_(HH) sequences, they may be suitably humanized, as further described herein. When the Nanobodies are partially humanized Nanobodies, they may optionally be further suitably humanized, again as described herein.

A Nanobody of the GLEW class may be an amino acid sequence that is comprised of four framework regions/sequences interrupted by three complementarity determining regions/sequences, in which

-   i) preferably, when the Nanobody of the GLEW-class is a     non-humanized Nanobody, the amino acid residue in position 108 is Q; -   ii) FR1 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-15 Representative FW1 sequences for Nanobodies of the GLEW-group. GLEW FW1 sequence no. 1 SEQ ID NO: 64 QVQLVESGGGLVQPGGSLRLSCAASGFTFS GLEW FW1 sequence no. 2 SEQ ID NO: 65 EVHLVESGGGLVRPGGSLRLSCAAFGFIFK GLEW FW1 sequence no. 3 SEQ ID NO: 66 QVKLEESGGGLAQPGGSLRLSCVASGFTFS GLEW FW1 sequence no. 4 SEQ ID NO: 67 EVQLVESGGGLVQPGGSLRLSCVCVSSGCT GLEW FW1 sequence no. 5 SEQ ID NO: 68 EVQLVESGGGLALPGGSLTLSCVFSGSTFS and in which:

-   iii) FR2 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-16 Representative FW2 sequences for Nanobodies of the GLEW-group. GLEW FW2 sequence no. 1 SEQ ID NO: 72 WVRQAPGKVLEWVS GLEW FW2 sequence no. 2 SEQ ID NO: 73 WVRRPPGKGLEWVS GLEW FW2 sequence no. 3 SEQ ID NO: 74 WVRQAPGMGLEWVS GLEW FW2 sequence no. 4 SEQ ID NO: 75 WVRQAPGKEPEWVS GLEW FW2 sequence no. 5 SEQ ID NO: 76 WVRQAPGKDQEWVS GLEW FW2 sequence no. 6 SEQ ID NO: 77 WVRQAPGKAEEWVS GLEW FW2 sequence no. 7 SEQ ID NO: 78 WVRQAPGKGLEWVA GLEW FW2 sequence no. 8 SEQ ID NO: 79 WVRQAPGRATEWVS and in which:

-   iv) FR3 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-17 Representative FW3 sequences for Nanobodies of the GLEW-group. GLEW FW3 sequence no. 1 SEQ ID NO: 80 RFTISRDNAKNTLYLQMNSLKPEDTAVYYCVK GLEW FW3 sequence no. 2 SEQ ID NO: 81 RFTISRDNARNTLYLQMDSLIPEDTALYYCAR GLEW FW3 sequence no. 3 SEQ ID NO: 82 RFTSSRDNAKSTLYLQMNDLKPEDTALYYCAR GLEW FW3 sequence no. 4 SEQ ID NO: 83 RFIISRDNAKNTLYLQMNSLGPEDTAMYYCQR GLEW FW3 sequence no. 5 SEQ ID NO: 84 RFTASRDNAKNTLYLQMNSLKSEDTARYYCAR GLEW FW3 sequence no. 6 SEQ ID NO: 85 RFTISRDNAKNTLYLQMDDLQSEDTAMYYCGR and in which:

-   v) FR4 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-18 Representative FW4 sequences for Nanobodies of the GLEW-group. GLEW FW4 sequence no. 1 SEQ ID NO: 86 GSQGTQVTVSS GLEW FW4 sequence no. 2 SEQ ID NO: 87 LRGGTQVTVSS GLEW FW4 sequence no. 3 SEQ ID NO: 88 RGQGTLVTVSS GLEW FW4 sequence no. 4 SEQ ID NO: 89 RSRGIQVTVSS GLEW FW4 sequence no. 5 SEQ ID NO: 90 WGKGTQVTVSS GLEW FW4 sequence no. 6 SEQ ID NO: 91 WGQGTQVTVSS and in which:

-   vi) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In the above Nanobodies, one or more of the further Hallmark residues are preferably as described herein (for example, when they are V_(HH) sequences or partially humanized Nanobodies).

With regard to framework 1, it will again be clear to the skilled person that, for determining the degree of amino acid identity, the amino acid residues on positions 1 to 4 and 27 to 30 are preferably disregarded.

In view of this, a Nanobody of the GLEW class may be an amino acid sequence that is comprised of four framework regions/sequences interrupted by three complementarity determining regions/sequences, in which:

-   i) preferably, when the Nanobody of the GLEW-class is a     non-humanized Nanobody, the amino acid residue in position 108 is Q;     and in which: -   ii) FR1 is an amino acid sequence that, on positions 5 to 26 of the     Kabat numbering, has at least 80% amino acid identity with at least     one of the following amino acid sequences:

TABLE A-19 Representative FW1 sequences (amino acid residues 5 to 26) for Nanobodies  of the KERE-group. GLEW FW1 sequence no. 6 SEQ ID NO: 69 VESGGGLVQPGGSLRLSCAASG GLEW FW1 sequence no. 7 SEQ ID NO: 70 EESGGGLAQPGGSLRLSCVASG GLEW FW1 sequence no. 8 SEQ ID NO: 71 VESGGGLALPGGSLTLSCVFSG and in which:

-   iii) FR2, FR3 and FR4 are as mentioned herein for FR2, FR3 and FR4     of Nanobodies of the GLEW-class;     and in which: -   iv) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

The above Nanobodies may for example be V_(HH) sequences or may be humanized Nanobodies. When the above Nanobody sequences are V_(HH) sequences, they may be suitably humanized, as further described herein. When the Nanobodies are partially humanized Nanobodies, they may optionally be further suitably humanized, again as described herein. In the above Nanobodies, one or more of the further Hallmark residues are preferably as described herein (for example, when they are V_(HH) sequences or partially humanized Nanobodies).

A Nanobody of the P, R, S 103 class may be an amino acid sequence that is comprised of four framework regions/sequences interrupted by three complementarity determining regions/sequences, in which

-   i) the amino acid residue at position 103 according to the Kabat     numbering is different from W;     and in which: -   ii) preferably the amino acid residue at position 103 according to     the Kabat numbering is P, R or S, and more preferably R;     and in which: -   iii) FR1 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-20 Representative FW1 sequences for Nanobodies of the P, R, S 103-group. P, R, S 103 FW1 sequence no. 1 SEQ ID NO: 92 AVQLVESGGGLVQAGGSLRLSCAASGRTFS P, R, S 103 FW1 sequence no. 2 SEQ ID NO: 93 QVQLQESGGGMVQPGGSLRLSCAASGFDFG P, R, S 103 FW1 sequence no. 3 SEQ ID NO: 94 EVHLVESGGGLVRPGGSLRLSCAAFGFIFK P, R, S 103 FW1 sequence no. 4 SEQ ID NO: 95 QVQLAESGGGLVQPGGSLKLSCAASRTIVS P, R, S 103 FW1 sequence no. 5 SEQ ID NO: 96 QEHLVESGGGLVDIGGSLRLSCAASERIFS P, R, S 103 FW1 sequence no. 6 SEQ ID NO: 97 QVKLEESGGGLAQPGGSLRLSCVASGFTFS P, R, S 103 FW1 sequence no. 7 SEQ ID NO: 98 EVQLVESGGGLVQPGGSLRLSCVCVSSGCT P, R, S 103 FW1 sequence no. 8 SEQ ID NO: 99 EVQLVESGGGLALPGGSLTLSCVFSGSTFS and in which

-   iv) FR2 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-21 Representative FW2 sequences for Nanobodies of the P, R, S 103-group. P, R, S 103 FW2 sequence no. 1 SEQ ID NO:102 WFRQAPGKEREFVA P, R, S 103 FW2 sequence no. 2 SEQ ID NO:103 WVRQAPGKVLEWVS P, R, S 103 FW2 sequence no. 3 SEQ ID NO:104 WVRRPPGKGLEWVS P, R, S 103 FW2 sequence no. 4 SEQ ID NO:105 WIRQAPGKEREGVS P, R, S 103 FW2 sequence no. 5 SEQ ID NO:106 WVRQYPGKEPEWVS P, R, S 103 FW2 sequence no. 6 SEQ ID NO:107 WFRQPPGKEHEFVA P, R, S 103 FW2 sequence no. 7 SEQ ID NO:108 WYRQAPGKRTELVA P, R, S 103 FW2 sequence no. 8 SEQ ID NO:109 WLRQAPGQGLEWVS P, R, S 103 FW2 sequence no. 9 SEQ ID NO:110 WLRQTPGKGLEWVG P, R, S 103 FW2 sequence no. 10 SEQ ID NO:111 WVRQAPGKAEEFVS and in which:

-   v) FR3 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-22 Representative FW3 sequences for Nanobodies of the P ,R, S 103-group. P, R, S 103 FW3 sequence no. 1 SEQ ID NO: 112 RFTISRDNAKNTVYLQMNSLKPEDTAVYYCAA P, R, S 103 FW3 sequence no. 2 SEQ ID NO: 113 RFTISRDNARNTLYLQMDSLIPEDTALYYCAR P, R, S 103 FW3 sequence no. 3 SEQ ID NO: 114 RFTISRDNAKNEMYLQMNNLKTEDTGVYWCGA P, R, S 103 FW3 sequence no. 4 SEQ ID NO: 115 RFTISSDSNRNMIYLQMNNLKPEDTAVYYCAA P, R, S 103 FW3 sequence no. 5 SEQ ID NO: 116 RFTISRDNAKNMLYLHLNNLKSEDTAVYYCRR P, R, S 103 FW3 sequence no. 6 SEQ ID NO: 117 RFTISRDNAKKTVYLRLNSLNPEDTAVYSCNL P, R, S 103 FW3 sequence no. 7 SEQ ID NO: 118 RFKISRDNAKKTLYLQMNSLGPEDTAMYYCQR P, R, S 103 FW3 sequence no. 8 SEQ ID NO: 119 RFTVSRDNGKNTAYLRMNSLKPEDTADYYCAV and in which:

-   vi) FR4 is an amino acid sequence that has at least 80% amino acid     identity with at least one of the following amino acid sequences:

TABLE A-23 Representative FW4 sequences for Nanobodies of the P, R, S 103-group. P, R, S 103 FW4 sequence no. 1 SEQ ID NO: 120 RGQGTQVTVSS P, R, S 103 FW4 sequence no. 2 SEQ ID NO: 121 LRGGTQVTVSS P, R, S 103 FW4 sequence no. 3 SEQ ID NO: 122 GNKGTLVTVSS P, R, S 103 FW4 sequence no. 4 SEQ ID NO: 123 SSPGTQVTVSS P, R, S 103 FW4 sequence no. 5 SEQ ID NO: 124 SSQGTLVTVSS P, R, S 103 FW4 sequence no. 6 SEQ ID NO: 125 RSRGIQVTVSS and in which:

-   vii) CDR1, CDR2 and CDR3 are as defined herein, and are preferably     as defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

In the above Nanobodies, one or more of the further Hallmark residues are preferably as described herein (for example, when they are V_(HH) sequences or partially humanized Nanobodies).

With regard to framework 1, it will again be clear to the skilled person that, for determining the degree of amino acid identity, the amino acid residues on positions 1 to 4 and 27 to 30 are preferably disregarded.

In view of this, a Nanobody of the P,R,S 103 class may be an amino acid sequence that is comprised of four framework regions/sequences interrupted by three complementarity determining regions/sequences, in which:

-   i) the amino acid residue at position 103 according to the Kabat     numbering is different from W;     and in which: -   ii) preferably the amino acid residue at position 103 according to     the Kabat numbering is P, R or S, and more preferably R;     and in which: -   iii) FR1 is an amino acid sequence that, on positions 5 to 26 of the     Kabat numbering, has at least 80% amino acid identity with at least     one of the following amino acid sequences:

TABLE A-24 Representative FW1 sequences (amino acid residues 5 to 26) for Nanobodies of the P, R, S 103-group. P, R, S 103 FW1 sequence no. 9 SEQ ID NO: 100 VESGGGLVQAGGSLRLSCAASG P, R, S 103 FW1 sequence no. 10 SEQ ID NO: 101 AESGGGLVQPGGSLKLSCAASR and in which:

-   iv) FR2, FR3 and FR4 are as mentioned herein for FR2, FR3 and FR4 of     Nanobodies of the P,R,S 103 class;     and in which: -   v) CDR1, CDR2 and CDR3 are as defined herein, and are preferably as     defined according to one of the preferred aspects herein, and are     more preferably as defined according to one of the more preferred     aspects herein.

The above Nanobodies may for example be V_(HH) sequences or may be humanized Nanobodies. When the above Nanobody sequences are V_(HH) sequences, they may be suitably humanized, as further described herein. When the Nanobodies are partially humanized Nanobodies, they may optionally be further suitably humanized, again as described herein.

In the above Nanobodies, one or more of the further Hallmark residues are preferably as described herein (for example, when they are V_(HH) sequences or partially humanized Nanobodies).

In another preferred, but non-limiting aspect, the invention relates to a Nanobody as described above, in which the CDR sequences have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said Nanobody and one or more of the sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239, in which the amino acid residues that form the framework regions are disregarded. Such Nanobodies can be as further described herein.

As already mentioned herein, another preferred but non-limiting aspect of the invention relates to a Nanobody with an amino acid sequence that is chosen from the group consisting of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 or from the group consisting of from amino acid sequences that have more than 80%, preferably more than 90%, more preferably more than 95%, such as 99% or more sequence identity (as defined herein) with at least one of the amino acid sequences of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239.

Also, in the above Nanobodies:

-   i) any amino acid substitution (when it is not a humanizing     substitution as defined herein) is preferably, and compared to the     corresponding amino acid sequence of SEQ ID NO's: 238 to 253, more     preferably SEQ ID NO: 238 and SEQ ID NO: 239, a conservative amino     acid substitution, (as defined herein);     and/or: -   ii) its amino acid sequence preferably contains either only amino     acid substitutions, or otherwise preferably no more than 5,     preferably no more than 3, and more preferably only 1 or 2 amino     acid deletions or insertions, compared to the corresponding amino     acid sequence of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO:     238 and SEQ ID NO: 239;     and/or -   iii) the CDR's may be CDR's that are derived by means of affinity     maturation, for example starting from the CDR's of to the     corresponding amino acid sequence of SEQ ID NO's: 238 to 253, more     preferably SEQ ID NO: 238 and SEQ ID NO: 239.

Preferably, the CDR sequences and FR sequences in the Nanobodies of the invention are such that the Nanobodies of the invention (and polypeptides of the invention comprising the same):

-   -   bind to hCXCR4 with a dissociation constant (K_(D)) of 10⁻⁵ to         10⁻¹² moles/liter or less, and preferably 10⁻⁷ to 10⁻¹²         moles/liter or less and more preferably 10⁻⁸ to 10⁻¹²         moles/liter (i.e. with an association constant (K_(A)) of 10⁵ to         10¹² liter/moles or more, and preferably 10⁷ to 10¹² liter/moles         or more and more preferably 10⁸ to 10¹² liter/moles);         and/or such that they:     -   bind to hCXCR4 with a k_(on)-rate of between 10² M⁻¹s⁻¹ to about         10⁷ M⁻¹s⁻¹, preferably between 10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more         preferably between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, such as between         10⁵ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹;         and/or such that they:     -   bind to hCXCR4 with a k_(off) rate between 1 s⁻¹         (t_(1/2)=0.69 s) and 10⁻⁶ s⁻¹ (providing a near irreversible         complex with a t_(1/2) of multiple days), preferably between         10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more preferably between 10⁻³ s⁻¹ and 10⁻⁶         s⁻¹, such as between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹.

Preferably, CDR sequences and FR sequences present in the Nanobodies of the invention are such that the Nanobodies of the invention will bind to Targets of the invention with an affinity less than 500 nM, preferably less than 200 nM, more preferably less than 10 nM, such as less than 500 pM.

In another preferred, but non-limiting aspect, the invention relates to a Nanobody as described above, in which the CDR sequences have at least 70% amino acid identity, preferably at least 80% amino acid identity, more preferably at least 90% amino acid identity, such as 95% amino acid identity or more or even essentially 100% amino acid identity with the CDR sequences of at least one of the amino acid sequences of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311. This degree of amino acid identity can for example be determined by determining the degree of amino acid identity (in a manner described herein) between said Nanobody and one or more of the sequences of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311, in which the amino acid residues that form the framework regions are disregarded. Such Nanobodies can be as further described herein.

As already mentioned herein, another preferred but non-limiting aspect of the invention relates to a Nanobody with an amino acid sequence that is chosen from the group consisting of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311 or from the group consisting of from amino acid sequences that have more than 80%, preferably more than 90%, more preferably more than 95%, such as 99% or more sequence identity (as defined herein) with at least one of the amino acid sequences of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311.

Also, in the above Nanobodies:

-   i) any amino acid substitution (when it is not a humanizing     substitution as defined herein) is preferably, and compared to the     corresponding amino acid sequence of SEQ ID NO's: 308 to 311, more     preferably SEQ ID NO: 311, a conservative amino acid substitution,     (as defined herein);     and/or: -   ii) its amino acid sequence preferably contains either only amino     acid substitutions, or otherwise preferably no more than 5,     preferably no more than 3, and more preferably only 1 or 2 amino     acid deletions or insertions, compared to the corresponding amino     acid sequence of SEQ ID NO's: 308 to 311, more preferably SEQ ID NO:     311;     and/or -   iii) the CDR's may be CDR's that are derived by means of affinity     maturation, for example starting from the CDR's of to the     corresponding amino acid sequence of SEQ ID NO's: 308 to 311, more     preferably SEQ ID NO: 311.

Preferably, the CDR sequences and FR sequences in the Nanobodies of the invention are such that the Nanobodies of the invention (and polypeptides of the invention comprising the same):

-   -   bind to hCD4 with a dissociation constant (K_(D)) of 10⁻⁵ to         10⁻¹² moles/liter or less, and preferably 10⁻⁷ to 10⁻¹²         moles/liter or less and more preferably 10⁻⁸ to 10⁻¹²         moles/liter (i.e. with an association constant (K_(A)) of 10⁵ to         10¹² liter/moles or more, and preferably 10⁷ to 10¹² liter/moles         or more and more preferably 10⁸ to 10¹² liter/moles);         and/or such that they:     -   bind to hCD4 with a k_(on)-rate of between 10² M⁻¹s⁻¹ to about         10⁷ M⁻¹s⁻¹, preferably between 10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more         preferably between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, such as between         10⁵ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹;         and/or such that they:     -   bind to hCD4 with a k_(off) rate between 1 s⁻¹ (t_(1/2)=0.69 s)         and 10⁻⁶ s⁻¹ (providing a near irreversible complex with a         t_(1/2) of multiple days), preferably between 10⁻² s⁻¹ and 10⁻⁶         s⁻¹, more preferably between 10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as         between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹.

Preferably, CDR sequences and FR sequences present in the Nanobodies of the invention are such that the Nanobodies of the invention will bind to Targets of the invention with an affinity less than 500 nM, preferably less than 200 nM, more preferably less than 10 nM, such as less than 500 pM.

According to one non-limiting aspect of the invention, a Nanobody may be as defined herein, but with the proviso that it has at least “one amino acid difference” (as defined herein) in at least one of the framework regions compared to the corresponding framework region of a naturally occurring human V_(H) domain, and in particular compared to the corresponding framework region of DP-47. More specifically, according to one non-limiting aspect of the invention, a Nanobody may be as defined herein, but with the proviso that it has at least “one amino acid difference” (as defined herein) at least one of the Hallmark residues (including those at positions 108, 103 and/or 45) compared to the corresponding framework region of a naturally occurring human V_(H) domain, and in particular compared to the corresponding framework region of DP-47. Usually, a Nanobody will have at least one such amino acid difference with a naturally occurring V_(H) domain in at least one of FR2 and/or FR4, and in particular at least one of the Hallmark residues in FR2 and/or FR4 (again, including those at positions 108, 103 and/or 45).

Also, a humanized Nanobody of the invention may be as defined herein, but with the proviso that it has at least “one amino acid difference” (as defined herein) in at least one of the framework regions compared to the corresponding framework region of a naturally occurring V_(HH) domain. More specifically, according to one non-limiting aspect of the invention, a humanized Nanobody may be as defined herein, but with the proviso that it has at least “one amino acid difference” (as defined herein) at least one of the Hallmark residues (including those at positions 108, 103 and/or 45) compared to the corresponding framework region of a naturally occurring V_(HH) domain. Usually, a humanized Nanobody will have at least one such amino acid difference with a naturally occurring V_(HH) domain in at least one of FR2 and/or FR4, and in particular at least one of the Hallmark residues in FR2 and/or FR4 (again, including those at positions 108, 103 and/or 45).

As will be clear from the disclosure herein, it is also within the scope of the invention to use natural or synthetic analogs, mutants, variants, alleles, homologs and orthologs (herein collectively referred to as “analogs”) of the Nanobodies of the invention as defined herein, and in particular analogs of the Nanobodies of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311. Thus, according to one aspect of the invention, the term “Nanobody of the invention” in its broadest sense also covers such analogs.

Generally, in such analogs, one or more amino acid residues may have been replaced, deleted and/or added, compared to the Nanobodies of the invention as defined herein. Such substitutions, insertions or deletions may be made in one or more of the framework regions and/or in one or more of the CDR's. When such substitutions, insertions or deletions are made in one or more of the framework regions, they may be made at one or more of the Hallmark residues and/or at one or more of the other positions in the framework residues, although substitutions, insertions or deletions at the Hallmark residues are generally less preferred (unless these are suitable humanizing substitutions as described herein).

By means of non-limiting examples, a substitution may for example be a conservative substitution (as described herein) and/or an amino acid residue may be replaced by another amino acid residue that naturally occurs at the same position in another V_(HH) domain (see Tables A-5 to A-8 for some non-limiting examples of such substitutions), although the invention is generally not limited thereto. Thus, any one or more substitutions, deletions or insertions, or any combination thereof, that either improve the properties of the Nanobody of the invention or that at least do not detract too much from the desired properties or from the balance or combination of desired properties of the Nanobody of the invention (i.e. to the extent that the Nanobody is no longer suited for its intended use) are included within the scope of the invention. A skilled person will generally be able to determine and select suitable substitutions, deletions or insertions, or suitable combinations of thereof, based on the disclosure herein and optionally after a limited degree of routine experimentation, which may for example involve introducing a limited number of possible substitutions and determining their influence on the properties of the Nanobodies thus obtained.

For example, and depending on the host organism used to express the Nanobody or polypeptide of the invention, such deletions and/or substitutions may be designed in such a way that one or more sites for post-translational modification (such as one or more glycosylation sites) are removed, as will be within the ability of the person skilled in the art. Alternatively, substitutions or insertions may be designed so as to introduce one or more sites for attachment of functional groups (as described herein), for example to allow site-specific pegylation (again as described herein).

As can be seen from the data on the V_(HH) entropy and V_(HH) variability given in Tables A-5 to A-8 above, some amino acid residues in the framework regions are more conserved than others. Generally, although the invention in its broadest sense is not limited thereto, any substitutions, deletions or insertions are preferably made at positions that are less conserved. Also, generally, amino acid substitutions are preferred over amino acid deletions or insertions.

The analogs are preferably such that they can bind to Targets of the invention with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein for the Nanobodies of the invention.

The analogs are preferably also such that they retain the favourable properties the Nanobodies, as described herein.

Also, according to one preferred aspect, the analogs have a degree of sequence identity of at least 70%, preferably at least 80%, more preferably at least 90%, such as at least 95% or 99% or more; and/or preferably have at most 20, preferably at most 10, even more preferably at most 5, such as 4, 3, 2 or only 1 amino acid difference (as defined herein), with one of the Nanobodies of SEQ ID NOs: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311.

Also, the framework sequences and CDR's of the analogs are preferably such that they are in accordance with the preferred aspects defined herein. More generally, as described herein, the analogs will have (a) a Q at position 108; and/or (b) a charged amino acid or a cysteine residue at position 45 and preferably an E at position 44, and more preferably E at position 44 and R at position 45; and/or (c) P, R or S at position 103.

One preferred class of analogs of the Nanobodies of the invention comprise Nanobodies that have been humanized (i.e. compared to the sequence of a naturally occurring Nanobody of the invention). As mentioned in the background art cited herein, such humanization generally involves replacing one or more amino acid residues in the sequence of a naturally occurring V_(HH) with the amino acid residues that occur at the same position in a human V_(H) domain, such as a human V_(H)3 domain. Examples of possible humanizing substitutions or combinations of humanizing substitutions will be clear to the skilled person, for example from the Tables herein, from the possible humanizing substitutions mentioned in the background art cited herein, and/or from a comparison between the sequence of a Nanobody and the sequence of a naturally occurring human V_(H) domain.

The humanizing substitutions should be chosen such that the resulting humanized Nanobodies still retain the favourable properties of Nanobodies as defined herein, and more preferably such that they are as described for analogs in the preceding paragraphs. A skilled person will generally be able to determine and select suitable humanizing substitutions or suitable combinations of humanizing substitutions, based on the disclosure herein and optionally after a limited degree of routine experimentation, which may for example involve introducing a limited number of possible humanizing substitutions and determining their influence on the properties of the Nanobodies thus obtained.

Generally, as a result of humanization, the Nanobodies of the invention may become more “human-like”, while still retaining the favorable properties of the Nanobodies of the invention as described herein. As a result, such humanized Nanobodies may have several advantages, such as a reduced immunogenicity, compared to the corresponding naturally occurring V_(HH) domains. Again, based on the disclosure herein and optionally after a limited degree of routine experimentation, the skilled person will be able to select humanizing substitutions or suitable combinations of humanizing substitutions which optimize or achieve a desired or suitable balance between the favourable properties provided by the humanizing substitutions on the one hand and the favourable properties of naturally occurring V_(HH) domains on the other hand.

The Nanobodies of the invention may be suitably humanized at any framework residue(s), such as at one or more Hallmark residues (as defined herein) or at one or more other framework residues (i.e. non-Hallmark residues) or any suitable combination thereof. One preferred humanizing substitution for Nanobodies of the “P,R,S-103 group” or the “KERE group” is Q108 into L108. Nanobodies of the “GLEW class” may also be humanized by a Q108 into L108 substitution, provided at least one of the other Hallmark residues contains a camelid (camelizing) substitution (as defined herein). For example, as mentioned above, one particularly preferred class of humanized Nanobodies has GLEW or a GLEW-like sequence at positions 44-47; P, R or S (and in particular R) at position 103, and an L at position 108.

The humanized and other analogs, and nucleic acid sequences encoding the same, can be provided in any manner known per se. For example, the analogs can be obtained by providing a nucleic acid that encodes a naturally occurring V_(HH) domain, changing the codons for the one or more amino acid residues that are to be substituted into the codons for the corresponding desired amino acid residues (e.g. by site-directed mutagenesis or by PCR using suitable mismatch primers), expressing the nucleic acid/nucleotide sequence thus obtained in a suitable host or expression system; and optionally isolating and/or purifying the analog thus obtained to provide said analog in essentially isolated form (e.g. as further described herein). This can generally be performed using methods and techniques known per se, which will be clear to the skilled person, for example from the handbooks and references cited herein, the background art cited herein and/or from the further description herein. Alternatively, a nucleic acid encoding the desired analog can be synthesized in a manner known per se (for example using an automated apparatus for synthesizing nucleic acid sequences with a predefined amino acid sequence) and can then be expressed as described herein. Yet another technique may involve combining one or more naturally occurring and/or synthetic nucleic acid sequences each encoding a part of the desired analog, and then expressing the combined nucleic acid sequence as described herein. Also, the analogs can be provided using chemical synthesis of the pertinent amino acid sequence using techniques for peptide synthesis known per se, such as those mentioned herein.

In this respect, it will be also be clear to the skilled person that the Nanobodies of the invention (including their analogs) can be designed and/or prepared starting from human V_(H) sequences (i.e. amino acid sequences or the corresponding nucleotide sequences), such as for example from human V_(H)3 sequences such as DP-47, DP-51 or DP-29, i.e. by introducing one or more camelizing substitutions (i.e. changing one or more amino acid residues in the amino acid sequence of said human V_(H) domain into the amino acid residues that occur at the corresponding position in a V_(HH) domain), so as to provide the sequence of a Nanobody of the invention and/or so as to confer the favourable properties of a Nanobody to the sequence thus obtained. Again, this can generally be performed using the various methods and techniques referred to in the previous paragraph, using an amino acid sequence and/or nucleotide sequence for a human V_(H) domain as a starting point.

Some preferred, but non-limiting camelizing substitutions can be derived from Tables A-5-A-8. It will also be clear that camelizing substitutions at one or more of the Hallmark residues will generally have a greater influence on the desired properties than substitutions at one or more of the other amino acid positions; although both and any suitable combination thereof are included within the scope of the invention. For example, it is possible to introduce one or more camelizing substitutions that already confer at least some the desired properties, and then to introduce further camelizing substitutions that either further improve said properties and/or confer additional favourable properties. Again, the skilled person will generally be able to determine and select suitable camelizing substitutions or suitable combinations of camelizing substitutions, based on the disclosure herein and optionally after a limited degree of routine experimentation, which may for example involve introducing a limited number of possible camelizing substitutions and determining whether the favourable properties of Nanobodies are obtained or improved (i.e. compared to the original V_(H) domain). Generally, however, such camelizing substitutions are preferably such that the resulting an amino acid sequence at least contains (a) a Q at position 108; and/or (b) a charged amino acid or a cysteine residue at position 45 and preferably also an E at position 44, and more preferably E at position 44 and Rat position 45; and/or (c) P, R or S at position 103; and optionally one or more further camelizing substitutions. More preferably, the camelizing substitutions are such that they result in a Nanobody of the invention and/or in an analog thereof (as defined herein), such as in a humanized analog and/or preferably in an analog that is as defined in the preceding paragraphs.

As will also be clear from the disclosure herein, it is also within the scope of the invention to use parts or fragments, or combinations of two or more parts or fragments, of the Nanobodies of the invention as defined herein, and in particular parts or fragments of the Nanobodies of SEQ ID NO's: 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311. Thus, according to one aspect of the invention, the term “Nanobody of the invention” in its broadest sense also covers such parts or fragments.

Generally, such parts or fragments of the Nanobodies of the invention (including analogs thereof) have amino acid sequences in which, compared to the amino acid sequence of the corresponding full length Nanobody of the invention (or analog thereof), one or more of the amino acid residues at the N-terminal end, one or more amino acid residues at the C-terminal end, one or more contiguous internal amino acid residues, or any combination thereof, have been deleted and/or removed.

The parts or fragments are preferably such that they can bind to Targets of the invention with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein for the Nanobodies of the invention.

Any part or fragment is preferably such that it comprises at least 10 contiguous amino acid residues, preferably at least 20 contiguous amino acid residues, more preferably at least 30 contiguous amino acid residues, such as at least 40 contiguous amino acid residues, of the amino acid sequence of the corresponding full length Nanobody of the invention.

Also, any part or fragment is such preferably that it comprises at least one of CDR1, CDR2 and/or CDR3 or at least part thereof (and in particular at least CDR3 or at least part thereof). More preferably, any part or fragment is such that it comprises at least one of the CDR's (and preferably at least CDR3 or part thereof) and at least one other CDR (i.e. CDR1 or CDR2) or at least part thereof, preferably connected by suitable framework sequence(s) or at least part thereof. More preferably, any part or fragment is such that it comprises at least one of the CDR's (and preferably at least CDR3 or part thereof) and at least part of the two remaining CDR's, again preferably connected by suitable framework sequence(s) or at least part thereof.

According to another particularly preferred, but non-limiting aspect, such a part or fragment comprises at least CDR3, such as FR3, CDR3 and FR4 of the corresponding full length Nanobody of the invention, i.e. as for example described in the International application WO 03/050531 (Lasters et al.).

As already mentioned above, it is also possible to combine two or more of such parts or fragments (i.e. from the same or different Nanobodies of the invention), i.e. to provide an analog (as defined herein) and/or to provide further parts or fragments (as defined herein) of a Nanobody of the invention. It is for example also possible to combine one or more parts or fragments of a Nanobody of the invention with one or more parts or fragments of a human V_(H) domain.

According to one preferred aspect, the parts or fragments have a degree of sequence identity of at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably at least 80%, such as at least 90%, 95% or 99% or more with one of the Nanobodies of SEQ ID NOs 238 to 253, more preferably SEQ ID NO: 238 and SEQ ID NO: 239 and SEQ ID NO's: 308 to 311, more preferably SEQ ID NO: 311.

The parts and fragments, and nucleic acid sequences encoding the same, can be provided and optionally combined in any manner known per se. For example, such parts or fragments can be obtained by inserting a stop codon in a nucleic acid that encodes a full-sized Nanobody of the invention, and then expressing the nucleic acid thus obtained in a manner known per se (e.g. as described herein). Alternatively, nucleic acids encoding such parts or fragments can be obtained by suitably restricting a nucleic acid that encodes a full-sized Nanobody of the invention or by synthesizing such a nucleic acid in a manner known per se. Parts or fragments may also be provided using techniques for peptide synthesis known per se.

The invention in its broadest sense also comprises derivatives of the Nanobodies of the invention. Such derivatives can generally be obtained by modification, and in particular by chemical and/or biological (e.g. enzymatical) modification, of the Nanobodies of the invention and/or of one or more of the amino acid residues that form the Nanobodies of the invention.

Examples of such modifications, as well as examples of amino acid residues within the Nanobody sequence that can be modified in such a manner (i.e. either on the protein backbone but preferably on a side chain), methods and techniques that can be used to introduce such modifications and the potential uses and advantages of such modifications will be clear to the skilled person.

For example, such a modification may involve the introduction (e.g. by covalent linking or in an other suitable manner) of one or more functional groups, residues or moieties into or onto the Nanobody of the invention, and in particular of one or more functional groups, residues or moieties that confer one or more desired properties or functionalities to the Nanobody of the invention. Example of such functional groups will be clear to the skilled person.

For example, such modification may comprise the introduction (e.g. by covalent binding or in any other suitable manner) of one or more functional groups that increase the half-life, the solubility and/or the absorption of the Nanobody of the invention, that reduce the immunogenicity and/or the toxicity of the Nanobody of the invention, that eliminate or attenuate any undesirable side effects of the Nanobody of the invention, and/or that confer other advantageous properties to and/or reduce the undesired properties of the Nanobodies and/or polypeptides of the invention; or any combination of two or more of the foregoing. Examples of such functional groups and of techniques for introducing them will be clear to the skilled person, and can generally comprise all functional groups and techniques mentioned in the general background art cited hereinabove as well as the functional groups and techniques known per se for the modification of pharmaceutical proteins, and in particular for the modification of antibodies or antibody fragments (including ScFv's and single domain antibodies), for which reference is for example made to Remington's Pharmaceutical Sciences. 16th ed., Mack Publishing Co., Easton, Pa. (1980). Such functional groups may for example be linked directly (for example covalently) to a Nanobody of the invention, or optionally via a suitable linker or spacer, as will again be clear to the skilled person.

One of the most widely used techniques for increasing the half-life and/or reducing the immunogenicity of pharmaceutical proteins comprises attachment of a suitable pharmacologically acceptable polymer, such as poly(ethyleneglycol) (PEG) or derivatives thereof (such as methoxypoly(ethyleneglycol) or mPEG). Generally, any suitable form of pegylation can be used, such as the pegylation used in the art for antibodies and antibody fragments (including but not limited to (single) domain antibodies and ScFv's); reference is made to for example Chapman, Nat. Biotechnol., 54, 531-545 (2002); by Veronese and Harris, Adv. Drug Deliv. Rev. 54, 453-456 (2003), by Harris and Chess, Nat. Rev. Drug. Discov. 2, (2003) and in WO 04/060965. Various reagents for pegylation of proteins are also commercially available, for example from Nektar Therapeutics, USA.

Preferably, site-directed pegylation is used, in particular via a cysteine-residue (see for example Yang et al., Protein Engineering, 16, 10, 761-770 (2003). For example, for this purpose, PEG may be attached to a cysteine residue that naturally occurs in a Nanobody of the invention, a Nanobody of the invention may be modified so as to suitably introduce one or more cysteine residues for attachment of PEG, or an amino acid sequence comprising one or more cysteine residues for attachment of PEG may be fused to the N- and/or C-terminus of a Nanobody of the invention, all using technique's of protein engineering known per se to the skilled person.

Preferably, for the Nanobodies and proteins of the invention, a PEG is used with a molecular weight of more than 5000, such as more than 10,000 and less than 200,000, such as less than 100,000; for example in the range of 20,000-80,000.

Another, usually less preferred modification comprises N-linked or O-linked glycosylation, usually as part of co-translational and/or post-translational modification, depending on the host cell used for expressing the Nanobody or polypeptide of the invention.

Yet another modification may comprise the introduction of one or more detectable labels or other signal-generating groups or moieties, depending on the intended use of the labelled Nanobody. Suitable labels and techniques for attaching, using and detecting them will be clear to the skilled person, and for example include, but are not limited to, fluorescent labels (such as fluorescein, isothiocyanate, rhodamine, phycoerythrin, phycocyanin, allophycocyanin, o-phthaldehyde, and fluorescamine and fluorescent metals such as ¹⁵²Eu or others metals from the lanthanide series), phosphorescent labels, chemiluminescent labels or bioluminescent labels (such as luminal, isoluminol, theromatic acridinium ester, imidazole, acridinium salts, oxalate ester, dioxetane or GFP and its analogs), radio-isotopes (such as ³H, ¹²⁵I, ³²P, ³⁵S, ¹⁴C, ⁵¹Cr, ³⁶Cl, ⁵⁷Co, ⁵⁸Co, ⁵⁹Fe, and ⁷⁵Se), metals, metal chelates or metallic cations (for example metallic cations such as ^(99m)Tc, ¹²³I, ¹¹¹In, ¹³¹I, ⁹⁷Ru, ⁶⁷Cu, ⁶⁷Ga, and ⁶⁸Ga or other metals or metallic cations that are particularly suited for use in in vivo, in vitro or in situ diagnosis and imaging, such as (¹⁵⁷Gd, ⁵⁵Mn, ¹⁶²Dy, ⁵²Cr, and ⁵⁶Fe), as well as chromophores and enzymes (such as malate dehydrogenase, staphylococcal nuclease, delta-V-steroid isomerase, yeast alcohol dehydrogenase, alpha-glycerophosphate dehydrogenase, triose phosphate isomerase, biotinavidin peroxidase, horseradish peroxidase, alkaline phosphatase, asparaginase, glucose oxidase, beta-galactosidase, ribonuclease, urease, catalase, glucose-VI-phosphate dehydrogenase, glucoamylase and acetylcholine esterase). Other suitable labels will be clear to the skilled person, and for example include moieties that can be detected using NMR or ESR spectroscopy.

Such labelled Nanobodies and polypeptides of the invention may for example be used for in vitro, in vivo or in situ assays (including immunoassays known per se such as ELISA, RIA, EIA and other “sandwich assays”, etc.) as well as in vivo diagnostic and imaging purposes, depending on the choice of the specific label.

As will be clear to the skilled person, another modification may involve the introduction of a chelating group, for example to chelate one of the metals or metallic cations referred to above. Suitable chelating groups for example include, without limitation, diethylenetriaminepentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA).

Yet another modification may comprise the introduction of a functional group that is one part of a specific binding pair, such as the biotin-(strept)avidin binding pair. Such a functional group may be used to link the Nanobody of the invention to another protein, polypeptide or chemical compound that is bound to the other half of the binding pair, i.e. through formation of the binding pair. For example, a Nanobody of the invention may be conjugated to biotin, and linked to another protein, polypeptide, compound or carrier conjugated to avidin or streptavidin. For example, such a conjugated Nanobody may be used as a reporter, for example in a diagnostic system where a detectable signal-producing agent is conjugated to avidin or streptavidin. Such binding pairs may for example also be used to bind the Nanobody of the invention to a carrier, including carriers suitable for pharmaceutical purposes. One non-limiting example are the liposomal formulations described by Cao and Suresh, Journal of Drug Targetting, 8, 4, 257 (2000). Such binding pairs may also be used to link a therapeutically active agent to the Nanobody of the invention.

For some applications, in particular for those applications in which it is intended to kill a cell that expresses the target against which the Nanobodies of the invention are directed (e.g. in the treatment of cancer), or to reduce or slow the growth and/or proliferation such a cell, the Nanobodies of the invention may also be linked to a toxin or to a toxic residue or moiety. Examples of toxic moieties, compounds or residues which can be linked to a Nanobody of the invention to provide—for example—a cytotoxic compound will be clear to the skilled person and can for example be found in the prior art cited above and/or in the further description herein. One example is the so-called ADEPT™ technology described in WO 03/055527.

Other potential chemical and enzymatical modifications will be clear to the skilled person. Such modifications may also be introduced for research purposes (e.g. to study function-activity relationships). Reference is for example made to Lundblad and Bradshaw, Biotechnol. Appl. Biochem., 26, 143-151 (1997).

Preferably, the derivatives are such that they bind to Targets of the invention with an affinity (suitably measured and/or expressed as a K_(D)-value (actual or apparent), a K_(A)-value (actual or apparent), a k_(on)-rate and/or a k_(off)-rate, or alternatively as an IC₅₀ value, as further described herein) that is as defined herein for the Nanobodies of the invention.

As mentioned above, the invention also relates to proteins or polypeptides that essentially consist of or comprise at least one Nanobody of the invention. By “essentially consist of” is meant that the amino acid sequence of the polypeptide of the invention either is exactly the same as the amino acid sequence of a Nanobody of the invention or corresponds to the amino acid sequence of a Nanobody of the invention which has a limited number of amino acid residues, such as 1-20 amino acid residues, for example 1-10 amino acid residues and preferably 1-6 amino acid residues, such as 1, 2, 3, 4, 5 or 6 amino acid residues, added at the amino terminal end, at the carboxy terminal end, or at both the amino terminal end and the carboxy terminal end of the amino acid sequence of the Nanobody.

Said amino acid residues may or may not change, alter or otherwise influence the (biological) properties of the Nanobody and may or may not add further functionality to the Nanobody. For example, such amino acid residues:

-   -   can comprise an N-terminal Met residue, for example as result of         expression in a heterologous host cell or host organism.     -   may form a signal sequence or leader sequence that directs         secretion of the Nanobody from a host cell upon synthesis.         Suitable secretory leader peptides will be clear to the skilled         person, and may be as further described herein. Usually, such a         leader sequence will be linked to the N-terminus of the         Nanobody, although the invention in its broadest sense is not         limited thereto;     -   may form a sequence or signal that allows the Nanobody to be         directed towards and/or to penetrate or enter into specific         organs, tissues, cells, or parts or compartments of cells,         and/or that allows the Nanobody to penetrate or cross a         biological barrier such as a cell membrane, a cell layer such as         a layer of epithelial cells, a tumor including solid tumors, or         the blood-brain-barrier. Examples of such amino acid sequences         will be clear to the skilled person. Some non-limiting examples         are the small peptide vectors (“Pep-trans vectors”) described in         WO 03/026700 and in Temsamani et al. Expert Opin. Biol.         Ther., I. 773 (2001); Temsamani and Vidal, Drug Discov. Today,         9, 1012 (004) and Rousselle, J. Pharmacal. Exp. Ther., 296,         124-131 (2001), and the membrane translocator sequence described         by Zhao et al., Apoptosis, 8, 631-637 (2003). C-terminal and         N-terminal amino acid sequences for intracellular targeting of         antibody fragments are for example described by Cardinale et         al., Methods, 34, 171 (2004). Other suitable techniques for         intracellular targeting involve the expression and/or use of         so-called “intrabodies” comprising a Nanobody of the invention,         as mentioned below;     -   may form a “tag”, for example an amino acid sequence or residue         that allows or facilitates the purification of the Nanobody, for         example using affinity techniques directed against said sequence         or residue. Thereafter, said sequence or residue may be removed         (e.g. by chemical or enzymatical cleavage) to provide the         Nanobody sequence (for this purpose, the tag may optionally be         linked to the Nanobody sequence via a cleavable linker sequence         or contain a cleavable motif). Some preferred, but non-limiting         examples of such residues are multiple histidine residues,         glutathione residues and a myc-tag (see for example SEQ ID NO:31         of WO 06/12282).     -   may be one or more amino acid residues that have been         functionalized and/or that can serve as a site for attachment of         functional groups. Suitable amino acid residues and functional         groups will be clear to the skilled person and include, but are         not limited to, the amino acid residues and functional groups         mentioned herein for the derivatives of the Nanobodies of the         invention.

According to another aspect, a polypeptide of the invention comprises a Nanobody of the invention, which is fused at its amino terminal end, at its carboxy terminal end, or both at its amino terminal end and at its carboxy terminal end to at least one further amino acid sequence, i.e. so as to provide a fusion protein comprising said Nanobody of the invention and the one or more further amino acid sequences. Such a fusion will also be referred to herein as a “Nanobody fusion”.

The one or more further amino acid sequence may be any suitable and/or desired amino acid sequences. The further amino acid sequences may or may not change, alter or otherwise influence the (biological) properties of the Nanobody, and may or may not add further functionality to the Nanobody or the polypeptide of the invention. Preferably, the further amino acid sequence is such that it confers one or more desired properties or functionalities to the Nanobody or the polypeptide of the invention.

For example, the further amino acid sequence may also provide a second binding site, which binding site may be directed against any desired protein, polypeptide, antigen, antigenic determinant or epitope (including but not limited to the same protein, polypeptide, antigen, antigenic determinant or epitope against which the Nanobody of the invention is directed, or a different protein, polypeptide, antigen, antigenic determinant or epitope).

Example of such amino acid sequences will be clear to the skilled person, and may generally comprise all amino acid sequences that are used in peptide fusions based on conventional antibodies and fragments thereof (including but not limited to ScFv's and single domain antibodies). Reference is for example made to the review by Holliger and Hudson, Nature Biotechnology, 23, 9, 1126-1136 (2005).

For example, such an amino acid sequence may be an amino acid sequence that increases the half-life, the solubility, or the absorption, reduces the immunogenicity or the toxicity, eliminates or attenuates undesirable side effects, and/or confers other advantageous properties to and/or reduces the undesired properties of the polypeptides of the invention, compared to the Nanobody of the invention per se. Some non-limiting examples of such amino acid sequences are serum proteins, such as human serum albumin (see for example WO 00/27435) or haptenic molecules (for example haptens that are recognized by circulating antibodies, see for example WO 98/22141).

In particular, it has been described in the art that linking fragments of immunoglobulins (such as V_(H) domains) to serum albumin or to fragments thereof can be used to increase the half-life. Reference is for made to WO 00/27435 and WO 01/077137). According to the invention, the Nanobody of the invention is preferably either directly linked to serum albumin (or to a suitable fragment thereof) or via a suitable linker, and in particular via a suitable peptide linked so that the polypeptide of the invention can be expressed as a genetic fusion (protein). According to one specific aspect, the Nanobody of the invention may be linked to a fragment of serum albumin that at least comprises the domain III of serum albumin or part thereof. Reference is for example made to WO 07/112940.

Alternatively, the further amino acid sequence may provide a second binding site or binding unit that is directed against a serum protein (such as, for example, human serum albumin or another serum protein such as IgG), so as to provide increased half-life in serum. Such amino acid sequences for example include the Nanobodies described below, as well as the small peptides and binding proteins described in WO 91/01743, WO 01/45746 and WO 02/076489 and the dAb's described in WO 03/002609 and WO 04/003019. Reference is also made to Harmsen et al., Vaccine, 23 (41); 4926-42, 2005, as well as to EP 0 368 684, as well as to WO 08/028,977, WO 08/043,821. WO 08/043,822.

Such amino acid sequences may in particular be directed against serum albumin (and more in particular human serum albumin) and/or against IgG (and more in particular human IgG). For example, such amino acid sequences may be amino acid sequences that are directed against (human) serum albumin and amino acid sequences that can bind to amino acid residues on (human) serum albumin that are not involved in binding of serum albumin to FcRn (see for example WO 06/0122787) and/or amino acid sequences that are capable of binding to amino acid residues on serum albumin that do not form part of domain III of serum albumin (see again for example WO 06/0122787); amino acid sequences that have or can provide an increased half-life (see for example WO 08/028,977); amino acid sequences against human serum albumin that are cross-reactive with serum albumin from at least one species of mammal, and in particular with at least one species of primate (such as, without limitation, monkeys from the genus Macaca (such as, and in particular, cynomolgus monkeys (Macaca fascicularis) and/or rhesus monkeys (Macaca mulatta)) and baboon (Papio ursinus), reference is again made to WO 08/028,977; amino acid sequences that can bind to serum albumin in a pH independent manner (see for example WO 08/043,821) and/or amino acid sequences that are conditional binders (see for example WO 08/043,822).

According to another aspect, the one or more further amino acid sequences may comprise one or more parts, fragments or domains of conventional 4-chain antibodies (and in particular human antibodies) and/or of heavy chain antibodies. For example, although usually less preferred, a Nanobody of the invention may be linked to a conventional (preferably human) V_(H) or V_(L) domain or to a natural or synthetic analog of a V_(H) or V_(L) domain, again optionally via a linker sequence (including but not limited to other (single) domain antibodies, such as the dAb's described by Ward et al.).

The at least one Nanobody may also be linked to one or more (preferably human) C_(H)1, C_(H)2 and/or C_(H)3 domains, optionally via a linker sequence. For instance, a Nanobody linked to a suitable C_(H)1 domain could for example be used—together with suitable light chains—to generate antibody fragments/structures analogous to conventional Fab fragments or F(ab′)₂ fragments, but in which one or (in case of an F(ab′)₂ fragment) one or both of the conventional V_(H) domains have been replaced by a Nanobody of the invention. Also, two Nanobodies could be linked to a C_(H)3 domain (optionally via a linker) to provide a construct with increased half-life in vivo.

According to one specific aspect of a polypeptide of the invention, one or more Nanobodies of the invention may be linked (optionally via a suitable linker or hinge region) to one or more constant domains (for example, 2 or 3 constant domains that can be used as part of/to form an Fc portion), to an Fc portion and/or to one or more antibody parts, fragments or domains that confer one or more effector functions to the polypeptide of the invention and/or may confer the ability to bind to one or more Fc receptors. For example, for this purpose, and without being limited thereto, the one or more further amino acid sequences may comprise one or more C_(H)2 and/or C_(H)3 domains of an antibody, such as from a heavy chain antibody (as described herein) and more preferably from a conventional human 4-chain antibody; and/or may form (part of) and Fc region, for example from IgG (e.g. from IgG1, IgG2, IgG3 or IgG4), from IgE or from another human Ig such as IgA, IgD or IgM. For example, WO 94/04678 describes heavy chain antibodies comprising a Camelid V_(HH) domain or a humanized derivative thereof (i.e. a Nanobody), in which the Camelidae C_(H)2 and/or C_(H)3 domain have been replaced by human C_(H)2 and C_(H)3 domains, so as to provide an immunoglobulin that consists of 2 heavy chains each comprising a Nanobody and human C_(H)2 and C_(H)3 domains (but no C_(H)1 domain), which immunoglobulin has the effector function provided by the C_(H)2 and C_(H)3 domains and which immunoglobulin can function without the presence of any light chains. Other amino acid sequences that can be suitably linked to the Nanobodies of the invention so as to provide an effector function will be clear to the skilled person, and may be chosen on the basis of the desired effector function(s). Reference is for example made to WO 04/058820, WO 99/42077, WO 02/056910, WO 09/068628 and WO 05/017148, as well as the review by Holliger and Hudson, supra. Coupling of a Nanobody of the invention to an Fc portion may also lead to an increased half-life, compared to the corresponding Nanobody of the invention. For some applications, the use of an Fc portion and/or of constant domains (i.e. C_(H)2 and/or C_(H)3 domains) that confer increased half-life without any biologically significant effector function may also be suitable or even preferred. Other suitable constructs comprising one or more Nanobodies and one or more constant domains with increased half-life in vivo will be clear to the skilled person, and may for example comprise two Nanobodies linked to a C_(H)3 domain, optionally via a linker sequence. Generally, any fusion protein or derivatives with increased half-life will preferably have a molecular weight of more than 50 kD, the cut-off value for renal absorption.

In another one specific, but non-limiting, aspect, in order to form a polypeptide of the invention, one or more amino acid sequences of the invention may be linked (optionally via a suitable linker or hinge region) to naturally occurring, synthetic or semisynthetic constant domains (or analogs, variants, mutants, parts or fragments thereof) that have a reduced (or essentially no) tendency to self-associate into dimers (i.e. compared to constant domains that naturally occur in conventional 4-chain antibodies). Such monomeric (i.e. not self-associating) Fc chain variants, or fragments thereof, will be clear to the skilled person. For example, Helm et al., J Biol Chem 1996 271 7494, describe monomeric Fcε chain variants that can be used in the polypeptide chains of the invention.

Also, such monomeric Fc chain variants are preferably such that they are still capable of binding to the complement or the relevant Fc receptor(s) (depending on the Fc portion from which they are derived), and/or such that they still have some or all of the effector functions of the Fc portion from which they are derived (or at a reduced level still suitable for the intended use). Alternatively, in such a polypeptide chain of the invention, the monomeric Fc chain may be used to confer increased half-life upon the polypeptide chain, in which case the monomeric Fc chain may also have no or essentially no effector functions.

Bivalent/multivalent, bispecific/multispecific or biparatopic/multiparatopic polypeptides of the invention may also be linked to Fc portions, in order to provide polypeptide constructs of the type that is described in WO 09/068630.

The further amino acid sequences may also form a signal sequence or leader sequence that directs secretion of the Nanobody or the polypeptide of the invention from a host cell upon synthesis (for example to provide a pre-, pro- or prepro-form of the polypeptide of the invention, depending on the host cell used to express the polypeptide of the invention).

The further amino acid sequence may also form a sequence or signal that allows the Nanobody or polypeptide of the invention to be directed towards and/or to penetrate or enter into specific organs, tissues, cells, or parts or compartments of cells, and/or that allows the Nanobody or polypeptide of the invention to penetrate or cross a biological barrier such as a cell membrane, a cell layer such as a layer of epithelial cells, a tumor including solid tumors, or the blood-brain-barrier. Suitable examples of such amino acid sequences will be clear to the skilled person, and for example include, but are not limited to, the “Peptrans” vectors mentioned above, the sequences described by Cardinale et al. and the amino acid sequences and antibody fragments known per se that can be used to express or produce the Nanobodies and polypeptides of the invention as so-called “intrabodies”, for example as described in WO 94/02610, WO 95/22618, U.S. Pat. No. 7,004,940, WO 03/014960, WO 99/07414; WO 05/01690; EP 1 512 696; and in Cattaneo, A. & Biocca, S. (1997) Intracellular Antibodies: Development and Applications. Landes and Springer-Verlag; and in Kontermann, Methods 34, (2004), 163-170, and the further references described therein.

For some applications, in particular for those applications in which it is intended to kill a cell that expresses the target against which the Nanobodies of the invention are directed (e.g. in the treatment of cancer), or to reduce or slow the growth and/or proliferation of such a cell, the Nanobodies of the invention may also be linked to a (cyto)toxic protein or polypeptide. Examples of such toxic proteins and polypeptides which can be linked to a Nanobody of the invention to provide—for example—a cytotoxic polypeptide of the invention will be clear to the skilled person and can for example be found in the prior art cited above and/or in the further description herein. One example is the so-called ADEPT™ technology described in WO 03/055527.

According to one preferred, but non-limiting aspect, said one or more further amino acid sequences comprise at least one further Nanobody, so as to provide a polypeptide of the invention that comprises at least two, such as three, four, five or more Nanobodies, in which said Nanobodies may optionally be linked via one or more linker sequences (as defined herein). Polypeptides of the invention that comprise two or more Nanobodies, of which at least one is a Nanobody of the invention, will also be referred to herein as “multivalent” polypeptides of the invention, and the Nanobodies present in such polypeptides will also be referred to herein as being in a “multivalent format”. For example a “bivalent” polypeptide of the invention comprises two Nanobodies, optionally linked via a linker sequence, whereas a “trivalent” polypeptide of the invention comprises three Nanobodies, optionally linked via two linker sequences; etc.; in which at least one of the Nanobodies present in the polypeptide, and up to all of the Nanobodies present in the polypeptide, is/are a Nanobody of the invention.

In a multivalent polypeptide of the invention, the two or more Nanobodies may be the same or different, and may be directed against the same antigen or antigenic determinant (for example against the same part(s) or epitope(s) or against different parts or epitopes) or may alternatively be directed against different antigens or antigenic determinants; or any suitable combination thereof. For example, a bivalent polypeptide of the invention may comprise (a) two identical Nanobodies; (b) a first Nanobody directed against a first antigenic determinant of a protein or antigen and a second Nanobody directed against the same antigenic determinant of said protein or antigen which is different from the first Nanobody; (c) a first Nanobody directed against a first antigenic determinant of a protein or antigen and a second Nanobody directed against another antigenic determinant of said protein or antigen; or (d) a first Nanobody directed against a first protein or antigen and a second Nanobody directed against a second protein or antigen (i.e. different from said first antigen). Similarly, a trivalent polypeptide of the invention may, for example and without being limited thereto, comprise (a) three identical Nanobodies; (b) two identical Nanobody against a first antigenic determinant of an antigen and a third Nanobody directed against a different antigenic determinant of the same antigen; (c) two identical Nanobody against a first antigenic determinant of an antigen and a third Nanobody directed against a second antigen different from said first antigen; (d) a first Nanobody directed against a first antigenic determinant of a first antigen, a second Nanobody directed against a second antigenic determinant of said first antigen and a third Nanobody directed against a second antigen different from said first antigen; or (e) a first Nanobody directed against a first antigen, a second Nanobody directed against a second antigen different from said first antigen, and a third Nanobody directed, against a third antigen different from said first and second antigen.

Multiparatopic

Polypeptides of the invention that contain at least two Nanobodies, in which at least one Nanobody is directed against a first antigen (i.e. against Targets of the invention) and at least one Nanobody is directed against a second antigen (i.e. different from Targets of the invention), will also be referred to as “multispecific” polypeptides of the invention, and the Nanobodies present in such polypeptides will also be referred to herein as being in a “multispecific format”. Thus, for example, a “bispecific” polypeptide of the invention is a polypeptide that comprises at least one Nanobody directed against a first antigen (i.e. Targets of the invention) and at least one further Nanobody directed against a second antigen (i.e. different from Targets of the invention), whereas a “trispecific” polypeptide of the invention is a polypeptide that comprises at least one Nanobody directed against a first antigen (i.e. Targets of the invention), at least one further Nanobody directed against a second antigen (i.e. different from Targets of the invention) and at least one further Nanobody directed against a third antigen (i.e. different from both Targets of the invention, and the second antigen); etc.

Accordingly, in its simplest form, a bispecific polypeptide of the invention is a bivalent polypeptide of the invention (as defined herein), comprising a first Nanobody directed against Targets of the invention, and a second Nanobody directed against a second antigen, in which said first and second Nanobody may optionally be linked via a linker sequence (as defined herein); whereas a trispecific polypeptide of the invention in its simplest form is a trivalent polypeptide of the invention (as defined herein), comprising a first Nanobody directed against Targets of the invention, a second Nanobody directed against a second antigen and a third Nanobody directed against a third antigen, in which said first, second and third Nanobody may optionally be linked via one or more, and in particular one and more, in particular two, linker sequences.

However, as will be clear from the description hereinabove, the invention is not limited thereto, in the sense that a multispecific polypeptide of the invention may comprise at least one Nanobody against Targets of the invention, and any number of Nanobodies directed against one or more antigens different from Targets of the invention.

Furthermore, although it is encompassed within the scope of the invention that the specific order or arrangement of the various Nanobodies in the polypeptides of the invention may have some influence on the properties of the final polypeptide of the invention (including but not limited to the affinity, specificity or avidity for Targets of the invention, or against the one or more other antigens), said order or arrangement is usually not critical and may be suitably chosen by the skilled person, optionally after some limited routine experiments based on the disclosure herein. Thus, when reference is made to a specific multivalent or multispecific polypeptide of the invention, it should be noted that this encompasses any order or arrangements of the relevant Nanobodies, unless explicitly indicated otherwise.

Finally, it is also within the scope of the invention that the polypeptides of the invention contain two or more Nanobodies and one or more further amino acid sequences (as mentioned herein).

For multivalent and multispecific polypeptides containing one or more V_(HH) domains and their preparation, reference is also made to Conrath et al., J. Biol. Chem., Vol. 276, 10. 7346-7350, 2001; Muyldermans, Reviews in Molecular Biotechnology 74 (2001), 277-302; as well as to for example WO 96/34103 and WO 99/23221. Some other examples of some specific multispecific and/or multivalent polypeptide of the invention can be found in the applications by Ablynx N.V. referred to herein.

One preferred, but non-limiting example of a multispecific polypeptide of the invention comprises at least one Nanobody of the invention and at least one Nanobody that provides for an increased half-life. Such Nanobodies may for example be Nanobodies that are directed against a serum protein, and in particular a human serum protein, such as human serum albumin, thyroxine-binding protein, (human) transferrin, fibrinogen, an immunoglobulin such as IgG, IgE or IgM, or against one of the serum proteins listed in WO 04/003019. Of these, Nanobodies that can bind to serum albumin (and in particular human serum albumin) or to IgG (and in particular human IgG, see for example Nanobody VH-1 described in the review by Muyldermans, supra) are particularly preferred (although for example, for experiments in mice or primates, Nanobodies against or cross-reactive with mouse serum albumin (MSA) or serum albumin from said primate, respectively, can be used. However, for pharmaceutical use, Nanobodies against human serum albumin or human IgG will usually be preferred). Nanobodies that provide for increased half-life and that can be used in the polypeptides of the invention include the Nanobodies directed against serum albumin that are described in WO 04/041865, in WO 06/122787 and in the further patent applications by Ablynx N.V., such as those mentioned above.

For example, the some preferred Nanobodies that provide for increased half-life for use in the present invention include Nanobodies that can bind to amino acid residues on (human) serum albumin that are not involved in binding of serum albumin to FcRn (see for example WO 06/0122787); Nanobodies that are capable of binding to amino acid residues on serum albumin that do not form part of domain III of serum albumin (see for example WO 06/0122787); Nanobodies that have or can provide an increased half-life (see for example WO 08/028,977); Nanobodies against human serum albumin that are cross-reactive with serum albumin from at least one species of mammal, and in particular with at least one species of primate (such as, without limitation, monkeys from the genus Macaca (such as, and in particular, cynomolgus monkeys (Maraca fascicularis) and/or rhesus monkeys (Macaca mulatta)) and baboon (Papio ursinus)) (see for example WO 08/028,977); Nanobodies that can bind to serum albumin in a pH independent manner (see for example WO 08/04382) and/or Nanobodies that are conditional binders (see for example WO 08/043822).

Some particularly preferred Nanobodies that provide for increased half-life and that can be used in the polypeptides of the invention include the Nanobodies ALB-1 to ALB-10 disclosed in WO 06/122787 (see Tables II and III) of which ALB-8 (SEQ ID NO: 62 in WO 06/122787) is particularly preferred.

According to a specific, but non-limiting aspect of the invention, the polypeptides of the invention contain, besides the one or more Nanobodies of the invention, at least one Nanobody against human serum albumin.

Generally, any polypeptides of the invention with increased half-life that contain one or more Nanobodies of the invention, and any derivatives of Nanobodies of the invention or of such polypeptides that have an increased half-life, preferably have a half-life that is at least 1.5 times, preferably at least 2 times, such as at least 5 times, for example at least 10 times or more than 20 times, greater than the half-life of the corresponding Nanobody of the invention per se. For example, such a derivative or polypeptides with increased half-life may have a half-life that is increased with more than 1 hours, preferably more than 2 hours, more preferably more than 6 hours, such as more than 12 hours, or even more than 24, 48 or 72 hours, compared to the corresponding Nanobody of the invention per se.

In a preferred, but non-limiting aspect of the invention, such derivatives or polypeptides may exhibit a serum half-life in human of at least about 12 hours, preferably at least 24 hours, more preferably at least 48 hours, even more preferably at least 72 hours or more. For example, such derivatives or polypeptides may have a half-life of at least 5 days (such as about 5 to 10 days), preferably at least 9 days (such as about 9 to 14 days), more preferably at least about 10 days (such as about 10 to 15 days), or at least about 11 days (such as about 11 to 16 days), more preferably at least about 12 days (such as about 12 to 18 days or more), or more than 14 days (such as about 14 to 19 days).

According to one aspect of the invention the polypeptides are capable of binding to one or more molecules which can increase the half-life of the polypeptide in vivo.

The polypeptides of the invention are stabilised in vivo and their half-life increased by binding to molecules which resist degradation and/or clearance or sequestration. Typically, such molecules are naturally occurring proteins which themselves have a long half-life in vivo.

Another preferred, but non-limiting example of a multispecific polypeptide of the invention comprises at least one Nanobody of the invention and at least one Nanobody that directs the polypeptide of the invention towards, and/or that allows the polypeptide of the invention to penetrate or to enter into specific organs, tissues, cells, or parts or compartments of cells, and/or that allows the Nanobody to penetrate or cross a biological barrier such as a cell membrane, a cell layer such as a layer of epithelial cells, a tumor including solid tumors, or the blood-brain-barrier. Examples of such Nanobodies include Nanobodies that are directed towards specific cell-surface proteins, markers or epitopes of the desired organ, tissue or cell (for example cell-surface markers associated with tumor cells), and the single-domain brain targeting antibody fragments described in WO 02/057445 and WO 06/040153, of which FC44 (SEQ ID NO: 189 of WO 06/040153) and FC5 (SEQ ID NO: 190 of WO 06/040154) are preferred examples.

In the polypeptides of the invention, the one or more Nanobodies and the one or more polypeptides may be directly linked to each other (as for example described in WO 99/23221) and/or may be linked to each other via one or more suitable spacers or linkers, or any combination thereof.

Suitable spacers or linkers for use in multivalent and multispecific polypeptides will be clear to the skilled person, and may generally be any linker or spacer used in the art to link amino acid sequences. Preferably, said linker or spacer is suitable for use in constructing proteins or polypeptides that are intended for pharmaceutical use.

Some particularly preferred spacers include the spacers and linkers that are used in the art to link antibody fragments or antibody domains. These include the linkers mentioned in the general background art cited above, as well as for example linkers that are used in the art to construct diabodies or ScFv fragments (in this respect, however, its should be noted that, whereas in diabodies and in ScFv fragments, the linker sequence used should have a length, a degree of flexibility and other properties that allow the pertinent V_(H) and V_(L) domains to come together to form the complete antigen-binding site, there is no particular limitation on the length or the flexibility of the linker used in the polypeptide of the invention, since each Nanobody by itself forms a complete antigen-binding site).

For example, a linker may be a suitable amino acid sequence, and in particular amino acid sequences of between 1 and 50, preferably between 1 and 30, such as between 1 and 10 amino acid residues. Some preferred examples of such amino acid sequences include gly-ser linkers, for example of the type (gly_(x)ser_(y))_(z), such as (for example (gly₄ser)₃ or (gly₃ser₂)₃, as described in WO 99/42077 and the GS30, GS15, GS9 and GS7 linkers described in the applications by Ablynx mentioned herein (see for example WO 06/040153 and WO 06/122825), as well as hinge-like regions, such as the hinge regions of naturally occurring heavy chain antibodies or similar sequences (such as described in WO 94/04678).

Some other particularly preferred linkers are poly-alanine (such as AAA), as well as the linkers GS30 (SEQ ID NO: 85 in WO 06/122825) and GS9 (SEQ ID NO: 84 in WO 06/122825).

Other suitable linkers generally comprise organic compounds or polymers, in particular those suitable for use in proteins for pharmaceutical use. For instance, poly(ethyleneglycol) moieties have been used to link antibody domains, see for example WO 04/081026.

It is encompassed within the scope of the invention that the length, the degree of flexibility and/or other properties of the linker(s) used (although not critical, as it usually is for linkers used in ScFv fragments) may have some influence on the properties of the final polypeptide of the invention, including but not limited to the affinity, specificity or avidity for Targets of the invention, or for one or more of the other antigens. Based on the disclosure herein, the skilled person will be able to determine the optimal linker(s) for use in a specific polypeptide of the invention, optionally after some limited routine experiments.

For example, in multivalent polypeptides of the invention that comprise Nanobodies directed against a multimeric antigen (such as a multimeric receptor or other protein), the length and flexibility of the linker are preferably such that it allows each Nanobody of the invention present in the polypeptide to bind to the antigenic determinant on each of the subunits of the multimer. Similarly, in a multispecific polypeptide of the invention that comprises Nanobodies directed against two or more different antigenic determinants on the same antigen (for example against different epitopes of an antigen and/or against different subunits of a multimeric receptor, channel or protein), the length and flexibility of the linker are preferably such that it allows each Nanobody to bind to its intended antigenic determinant. Again, based on the disclosure herein, the skilled person will be able to determine the optimal linker(s) for use in a specific polypeptide of the invention, optionally after some limited routine experiments.

It is also within the scope of the invention that the linker(s) used confer one or more other favourable properties or functionality to the polypeptides of the invention, and/or provide one or more sites for the formation of derivatives and/or for the attachment of functional groups (e.g. as described herein for the derivatives of the Nanobodies of the invention). For example, linkers containing one or more charged amino acid residues (see Table A-2 above) can provide improved hydrophilic properties, whereas linkers that form or contain small epitopes or tags can be used for the purposes of detection, identification and/or purification. Again, based on the disclosure herein, the skilled person will be able to determine the optimal linkers for use in a specific polypeptide of the invention, optionally after some limited routine experiments.

Finally, when two or more linkers are used in the polypeptides of the invention, these linkers may be the same or different. Again, based on the disclosure herein, the skilled person will be able to determine the optimal linkers for use in a specific polypeptide of the invention, optionally after some limited routine experiments.

Usually, for easy of expression and production, a polypeptide of the invention will be a linear polypeptide. However, the invention in its broadest sense is not limited thereto. For example, when a polypeptide of the invention comprises three of more Nanobodies, it is possible to link them by use of a linker with three or more “arms”, which each “arm” being linked to a Nanobody, so as to provide a “star-shaped” construct. It is also possible, although usually less preferred, to use circular constructs.

The invention also comprises derivatives of the polypeptides of the invention, which may be essentially analogous to the derivatives of the Nanobodies of the invention, i.e. as described herein.

The invention also comprises proteins or polypeptides that “essentially consist” of a polypeptide of the invention (in which the wording “essentially consist of” has essentially the same meaning as indicated hereinabove).

According to one aspect of the invention, the polypeptide of the invention is in essentially isolated from, as defined herein.

The amino acid sequences, Nanobodies, polypeptides and nucleic acids of the invention can be prepared in a manner known per se, as will be clear to the skilled person from the further description herein. For example, the Nanobodies and polypeptides of the invention can be prepared in any manner known per se for the preparation of antibodies and in particular for the preparation of antibody fragments (including but not limited to (single) domain antibodies and ScFv fragments). Some preferred, but non-limiting methods for preparing the amino acid sequences, Nanobodies, polypeptides and nucleic acids include the methods and techniques described herein.

As will be clear to the skilled person, one particularly useful method for preparing an amino acid sequence, Nanobody and/or a polypeptide of the invention generally comprises the steps of:

-   i) the expression, in a suitable host cell or host organism (also     referred to herein as a “host of the invention”) or in another     suitable expression system of a nucleic acid that encodes said amino     acid sequence, Nanobody or polypeptide of the invention (also     referred to herein as a “nucleic acid of the invention”), optionally     followed by: -   ii) isolating and/or purifying the amino acid sequence, Nanobody or     polypeptide of the invention thus obtained.

In particular, such a method may comprise the steps of:

-   i) cultivating and/or maintaining a host of the invention under     conditions that are such that said host of the invention expresses     and/or produces at least one amino acid sequence, Nanobody and/or     polypeptide of the invention; optionally followed by: -   ii) isolating and/or purifying the amino acid sequence, Nanobody or     polypeptide of the invention thus obtained.

A nucleic acid of the invention can be in the form of single or double stranded DNA or RNA, and is preferably in the form of double stranded DNA. For example, the nucleotide sequences of the invention may be genomic DNA, cDNA or synthetic DNA (such as DNA with a codon usage that has been specifically adapted for expression in the intended host cell or host organism).

According to one aspect of the invention, the nucleic acid of the invention is in essentially isolated from, as defined herein.

The nucleic acid of the invention may also be in the form of, be present in and/or be part of a vector, such as for example a plasmid, cosmid or YAC, which again may be in essentially isolated form.

The nucleic acids of the invention can be prepared or obtained in a manner known per se, based on the information on the amino acid sequences for the polypeptides of the invention given herein, and/or can be isolated from a suitable natural source. To provide analogs, nucleotide sequences encoding naturally occurring V_(HH) domains can for example be subjected to site-directed mutagenesis, so at to provide a nucleic acid of the invention encoding said analog. Also, as will be clear to the skilled person, to prepare a nucleic acid of the invention, also several nucleotide sequences, such as at least one nucleotide sequence encoding a Nanobody and for example nucleic acids encoding one or more linkers can be linked together in a suitable manner.

Techniques for generating the nucleic acids of the invention will be clear to the skilled person and may for instance include, but are not limited to, automated DNA synthesis; site-directed mutagenesis; combining two or more naturally occurring and/or synthetic sequences (or two or more parts thereof), introduction of mutations that lead to the expression of a truncated expression product; introduction of one or more restriction sites (e.g. to create cassettes and/or regions that may easily be digested and/or ligated using suitable restriction enzymes), and/or the introduction of mutations by means of a PCR reaction using one or more “mismatched” primers, using for example a sequence of a naturally occurring form of Targets of the invention as a template. These and other techniques will be clear to the skilled person, and reference is again made to the standard handbooks, such as Sambrook et al. and Ausubel et al., mentioned above, as well as the Examples below.

The nucleic acid of the invention may also be in the form of, be present in and/or be part of a genetic construct, as will be clear to the person skilled in the art. Such genetic constructs generally comprise at least one nucleic acid of the invention that is optionally linked to one or more elements of genetic constructs known per se, such as for example one or more suitable regulatory elements (such as a suitable promoter(s), enhancer(s), terminator(s), etc.) and the further elements of genetic constructs referred to herein. Such genetic constructs comprising at least one nucleic acid of the invention will also be referred to herein as “genetic constructs of the invention”.

The genetic constructs of the invention may be DNA or RNA, and are preferably double-stranded DNA. The genetic constructs of the invention may also be in a form suitable for transformation of the intended host cell or host organism, in a form suitable for integration into the genomic DNA of the intended host cell or in a form suitable for independent replication, maintenance and/or inheritance in the intended host organism. For instance, the genetic constructs of the invention may be in the form of a vector, such as for example a plasmid, cosmid, YAC, a viral vector or transposon. In particular, the vector may be an expression vector, i.e. a vector that can provide for expression in vitro and/or in vivo (e.g. in a suitable host cell, host organism and/or expression system).

In a preferred but non-limiting aspect, a genetic construct of the invention comprises

-   i) at least one nucleic acid of the invention; operably connected to -   ii) one or more regulatory elements, such as a promoter and     optionally a suitable terminator;     and optionally also -   iii) one or more further elements of genetic constructs known per     se;     in which the terms “regulatory element”, “promoter”, “terminator”     and “operably connected” have their usual meaning in the art (as     further described herein); and in which said “further elements”     present in the genetic constructs may for example be 3′- or 5′-UTR     sequences, leader sequences, selection markers, expression     markers/reporter genes, and/or elements that may facilitate or     increase (the efficiency of) transformation or integration. These     and other suitable elements for such genetic constructs will be     clear to the skilled person, and may for instance depend upon the     type of construct used, the intended host cell or host organism; the     manner in which the nucleotide sequences of the invention of     interest are to be expressed (e.g. via constitutive, transient or     inducible expression); and/or the transformation technique to be     used. For example, regulatory sequences, promoters and terminators     known per se for the expression and production of antibodies and     antibody fragments (including but not limited to (single) domain     antibodies and ScFv fragments) may be used in an essentially     analogous manner.

Preferably, in the genetic constructs of the invention, said at least one nucleic acid of the invention and said regulatory elements, and optionally said one or more further elements, are “operably linked” to each other, by which is generally meant that they are in a functional relationship with each other. For instance, a promoter is considered “operably linked” to a coding sequence if said promoter is able to initiate or otherwise control/regulate the transcription and/or the expression of a coding sequence (in which said coding sequence should be understood as being “under the control of” said promoter). Generally, when two nucleotide sequences are operably linked, they will be in the same orientation and usually also in the same reading frame. They will usually also be essentially contiguous, although this may also not be required.

Preferably, the regulatory and further elements of the genetic constructs of the invention are such that they are capable of providing their intended biological function in the intended host cell or host organism.

For instance, a promoter, enhancer or terminator should be “operable” in the intended host cell or host organism, by which is meant that (for example) said promoter should be capable of initiating or otherwise controlling/regulating the transcription and/or the expression of a nucleotide sequence—e.g. a coding sequence—to which it is operably linked (as defined herein).

Some particularly preferred promoters include, but are not limited to, promoters known per se for the expression in the host cells mentioned herein; and in particular promoters for the expression in the bacterial cells, such as those mentioned herein and/or those used in the Examples.

A selection marker should be such that it allows—i.e. under appropriate selection conditions—host cells and/or host organisms that have been (successfully) transformed with the nucleotide sequence of the invention to be distinguished from host cells/organisms that have not been (successfully) transformed. Some preferred, but non-limiting examples of such markers are genes that provide resistance against antibiotics (such as kanamycin or ampicillin), genes that provide for temperature resistance, or genes that allow the host cell or host organism to be maintained in the absence of certain factors, compounds and/or (food) components in the medium that are essential for survival of the non-transformed cells or organisms.

A leader sequence should be such that—in the intended host cell or host organism—it allows for the desired post-translational modifications and/or such that it directs the transcribed mRNA to a desired part or organelle of a cell. A leader sequence may also allow for secretion of the expression product from said cell. As such, the leader sequence may be any pro-, pre-, or prepro-sequence operable in the host cell or host organism. Leader sequences may not be required for expression in a bacterial cell. For example, leader sequences known per se for the expression and production of antibodies and antibody fragments (including but not limited to single domain antibodies and ScFv fragments) may be used in an essentially analogous manner.

An expression marker or reporter gene should be such that—in the host cell or host organism—it allows for detection of the expression of (a gene or nucleotide sequence present on) the genetic construct. An expression marker may optionally also allow for the localisation of the expressed product, e.g. in a specific part or organelle of a cell and/or in (a) specific cell(s), tissue(s), organ(s) or part(s) of a multicellular organism. Such reporter genes may also be expressed as a protein fusion with the amino acid sequence of the invention. Some preferred, but non-limiting examples include fluorescent proteins such as GFP.

Some preferred, but non-limiting examples of suitable promoters, terminator and further elements include those that can be used for the expression in the host cells mentioned herein; and in particular those that are suitable for expression in bacterial cells, such as those mentioned herein and/or those used in the Examples below. For some (further) non-limiting examples of the promoters, selection markers, leader sequences, expression markers and further elements that may be present/used in the genetic constructs of the invention—such as terminators, transcriptional and/or translational enhancers and/or integration factors—reference is made to the general handbooks such as Sambrook et al. and Ausubel et al. mentioned above, as well as to the examples that are given in WO 95/07463, WO 96/23810, WO 95/07463, WO 95/21191, WO 97/11094, WO 97/42320, WO 98/06737, WO 98/21355, U.S. Pat. No. 7,207,410, U.S. Pat. No. 5,693,492 and EP 1 085 089. Other examples will be clear to the skilled person. Reference is also made to the general background art cited above and the further references cited herein.

The genetic constructs of the invention may generally be provided by suitably linking the nucleotide sequence(s) of the invention to the one or more further elements described above, for example using the techniques described in the general handbooks such as Sambrook et al. and Ausubel et al., mentioned above.

Often, the genetic constructs of the invention will be obtained by inserting a nucleotide sequence of the invention in a suitable (expression) vector known per se. Some preferred, but non-limiting examples of suitable expression vectors are those used in the Examples below, as well as those mentioned herein.

The nucleic acids of the invention and/or the genetic constructs of the invention may be used to transform a host cell or host organism, i.e. for expression and/or production of the amino acid sequence, Nanobody or polypeptide of the invention. Suitable hosts or host cells will be clear to the skilled person, and may for example be any suitable fungal, prokaryotic or eukaryotic cell or cell line or any suitable fungal, prokaryotic or eukaryotic organism, for example:

-   -   a bacterial strain, including but not limited to gram-negative         strains such as strains of Escherichia coli; of Proteus, for         example of Proteus mirabilis; of Pseudomonas, for example of         Pseudomonas fluorescens; and gram-positive strains such as         strains of Bacillus, for example of Bacillus subtilis or of         Bacillus brevis; of Streptomyces, for example of Streptomyces         lividans; of Staphylococcus, for example of Staphylococcus         carnosus; and of Lactococcus, for example of Lactococcus lactis;     -   a fungal cell, including but not limited to cells from species         of Trichoderma, for example from Trichoderma reesei; of         Neurospora, for example from Neurospora crassa; of Sordaria, for         example from Sordaria macrospora; of Aspergillus, for example         from Aspergillus niger or from Aspergillus sojae; or from other         filamentous fungi;     -   a yeast cell, including but not limited to cells from species of         Saccharomyces, for example of Saccharomyces cerevisiae; of         Schizosaccharomyces, for example of Schizosaccharomyces pompe;         of Pichia, for example of Pichia pastoris or of Pichia         methanolica; of Hansenula, for example of Hansenula polymorpha;         of Kluyveromyces, for example of Kluyveromyces lactis; of         Arxula, for example of Arxula adeninivorans; of Yarrowia, for         example of Yarrowia lipolytica;     -   an amphibian cell or cell line, such as Xenopus oocytes;     -   an insect-derived cell or cell line, such as cells/cell lines         derived from lepidoptera, including but not limited to         Spodoptera SF9 and Sf21 cells or cells/cell lines derived from         Drosophila, such as Schneider and Kc cells;     -   a plant or plant cell, for example in tobacco plants; and/or     -   a mammalian cell or cell line, for example a cell or cell line         derived from a human, a cell or a cell line from mammals         including but not limited to CHO-cells, BHK-cells (for example         BHK-21 cells) and human cells or cell lines such as HeLa, COS         (for example COS-7) and PER.C6 cells;         as well as all other hosts or host cells known per se for the         expression and production of antibodies and antibody fragments         (including but not limited to (single) domain antibodies and         ScFv fragments), which will be clear to the skilled person.         Reference is also made to the general background art cited         hereinabove, as well as to for example WO 94/29457; WO 96/34103;         WO 99/42077; Frenken et al., (1998), supra; Riechmann and         Muyldermans, (1999), supra; van der Linden, (2000), supra;         Thomassen et al., (2002), supra; Joosten et al., (2003), supra;         Joosten et al., (2005), supra; and the further references cited         herein.

The amino acid sequences, Nanobodies and polypeptides of the invention can also be introduced and expressed in one or more cells, tissues or organs of a multicellular organism, for example for prophylactic and/or therapeutic purposes (e.g. as a gene therapy). For this purpose, the nucleotide sequences of the invention may be introduced into the cells or tissues in any suitable way, for example as such (e.g. using liposomes) or after they have been inserted into a suitable gene therapy vector (for example derived from retroviruses such as adenovirus, or parvoviruses such as adeno-associated virus). As will also be clear to the skilled person, such gene therapy may be performed in vivo and/or in situ in the body of a patient by administering a nucleic acid of the invention or a suitable gene therapy vector encoding the same to the patient or to specific cells or a specific tissue or organ of the patient; or suitable cells (often taken from the body of the patient to be treated, such as explanted lymphocytes, bone marrow aspirates or tissue biopsies) may be treated in vitro with a nucleotide sequence of the invention and then be suitably (re-)introduced into the body of the patient. All this can be performed using gene therapy vectors, techniques and delivery systems which are well known to the skilled person, and for example described in Culver. K. W., “Gene Therapy”, 1994, p. xii, Mary Ann Liebert, Inc., Publishers, New York, N.Y); Giordano, Nature F Medicine 2 (1996), 534-539; Schaper, Circ. Res. 79 (1996), 911-919; Anderson, Science 256 (1992), 808-813; Verma, Nature 389 (1994), 239; Isner, Lancet 348 (1996), 370-374; Muhlhauser, Circ. Res. 77 (1995), 1077-1086; Onodera, Blood 91; (1998), 30-36; Verma, Gene Ther. 5 (1998), 692-699; Nabel, Ann. N.Y. Acad. Sci.: 811 (1997), 289-292; Verzeletti, Hum. Gene Ther. 9 (1998), 2243-51; Wang, Nature Medicine 2 (1996), 714-716; WO 94/29469; WO 97/00957, U.S. Pat. No. 5,580,859; U.S. Pat. No. 55,895,466; or Schaper, Current Opinion in Biotechnology 7 (1996), 635-640. For example, in situ expression of ScFv fragments (Afanasieva et al., Gene Ther., 10, 1850-1859 (2003)) and of diabodies (Blanco et al., J. Immunol, 171, 1070-1077 (2003)) has been described in the art.

For expression of the Nanobodies in a cell, they may also be expressed as so-called “intrabodies”, as for example described in WO 94/02610, WO 95/22618 and U.S. Pat. No. 7,004,940; WO 03/014960: in Cattaneo, A. & Biocca, S. (1997) Intracellular Antibodies: Development and Applications. Landes and Springer-Verlag; and in Kontermann, Methods 34, (2004), 163-170.

The amino acid sequences, Nanobodies and polypeptides of the invention can for example also be produced in the milk of transgenic mammals, for example in the milk of rabbits, cows, goats or sheep (see for example U.S. Pat. No. 6,741,957, U.S. Pat. No. 6,304,489 and U.S. Pat. No. 6,849,992 for general techniques for introducing transgenes into mammals), in plants or parts of plants including but not limited to their leaves, flowers, fruits, seed, roots or tubers (for example in tobacco, maize, soybean or alfalfa) or in for example pupae of the silkworm Bombix mori.

Furthermore, the amino acid sequences, Nanobodies and polypeptides of the invention can also be expressed and/or produced in cell-free expression systems, and suitable examples of such systems will be clear to the skilled person. Some preferred, but non-limiting examples include expression in the wheat germ system; in rabbit reticulocyte lysates; or in the E. coli Zubay system.

As mentioned above, one of the advantages of the use of Nanobodies is that the polypeptides based thereon can be prepared through expression in a suitable bacterial system, and suitable bacterial expression systems, vectors, host cells, regulatory elements, etc., will be clear to the skilled person, for example from the references cited above. It should however be noted that the invention in its broadest sense is not limited to expression in bacterial systems.

Preferably, in the invention, an (in vivo or in vitro) expression system, such as a bacterial expression system, is used that provides the polypeptides of the invention in a form that is suitable for pharmaceutical use, and such expression systems will again be clear to the skilled person. As also will be clear to the skilled person, polypeptides of the invention suitable for pharmaceutical use can be prepared using techniques for peptide synthesis.

For production on industrial scale, preferred heterologous hosts for the (industrial) production of Nanobodies or Nanobody-containing protein therapeutics include strains of E. coli, Pichia pastoris, S. cerevisiae that are suitable for large scale expression/production/fermentation, and in particular for large scale pharmaceutical (i.e. GMP grade) expression/production/fermentation. Suitable examples of such strains will be clear to the skilled person. Such strains and production/expression systems are also made available by companies such as Biovitrum (Uppsala, Sweden).

Alternatively, mammalian cell lines, in particular Chinese hamster ovary (CHO) cells, can be used for large scale expression/production/fermentation, and in particular for large scale pharmaceutical expression/production/fermentation. Again, such expression/production systems are also made available by some of the companies mentioned above.

The choice of the specific expression system would depend in part on the requirement for certain post-translational modifications, more specifically glycosylation. The production of a Nanobody-containing recombinant protein for which glycosylation is desired or required would necessitate the use of mammalian expression hosts that have the ability to glycosylate the expressed protein. In this respect, it will be clear to the skilled person that the glycosylation pattern obtained (i.e. the kind, number and position of residues attached) will depend on the cell or cell line that is used for the expression. Preferably, either a human cell or cell line is used (i.e. leading to a protein that essentially has a human glycosylation pattern) or another mammalian cell line is used that can provide a glycosylation pattern that is essentially and/or functionally the same as human glycosylation or at least mimics human glycosylation. Generally, prokaryotic hosts such as E. coli do not have the ability to glycosylate proteins, and the use of lower eukaryotes such as yeast usually leads to a glycosylation pattern that differs from human glycosylation. Nevertheless, it should be understood that all the foregoing host cells and expression systems can be used in the invention, depending on the desired amino acid sequence, Nanobody or polypeptide to be obtained.

Thus, according to one non-limiting aspect of the invention, the amino acid sequence, Nanobody or polypeptide of the invention is glycosylated. According to another non-limiting aspect of the invention, the amino acid sequence, Nanobody or polypeptide of the invention is non-glycosylated.

According to one preferred, but non-limiting aspect of the invention, the amino acid sequence, Nanobody or polypeptide of the invention is produced in a bacterial cell, in particular a bacterial cell suitable for large scale pharmaceutical production, such as cells of the strains mentioned above.

According to another preferred, but non-limiting aspect of the invention, the amino acid sequence, Nanobody or polypeptide of the invention is produced in a yeast cell, in particular a yeast cell suitable for large scale pharmaceutical production, such as cells of the species mentioned above.

According to yet another preferred, but non-limiting aspect of the invention, the amino acid sequence, Nanobody or polypeptide of the invention is produced in a mammalian cell, in particular in a human cell or in a cell of a human cell line, and more in particular in a human cell or in a cell of a human cell line that is suitable for large scale pharmaceutical production, such as the cell lines mentioned hereinabove.

When expression in a host cell is used to produce the amino acid sequences, Nanobodies and the polypeptides of the invention, the amino acid sequences, Nanobodies and polypeptides of the invention can be produced either intracellullarly (e.g. in the cytosol, in the periplasms or in inclusion bodies) and then isolated from the host cells and optionally further purified; or can be produced extracellularly (e.g. in the medium in which the host cells are cultured) and then isolated from the culture medium and optionally further purified. When eukaryotic host cells are used, extracellular production is usually preferred since this considerably facilitates the further isolation and downstream processing of the Nanobodies and proteins obtained. Bacterial cells such as the strains of E. coli mentioned above normally do not secrete proteins extracellularly, except for a few classes of proteins such as toxins and homolysin, and secretory production in E. coli refers to the translocation of proteins across the inner membrane to the periplasmic space. Periplasmic production provides several advantages over cytosolic production. For example, the N-terminal amino acid sequence of the secreted product can be identical to the natural gene product after cleavage of the secretion signal sequence by a specific signal peptidase. Also, there appears to be much less protease activity in the periplasm than in the cytoplasm. In addition, protein purification is simpler due to fewer contaminating proteins in the periplasm. Another advantage is that correct disulfide bonds may form because the periplasm provides a more oxidative environment than the cytoplasm. Proteins overexpressed in E. coli are often found in insoluble aggregates, so-called inclusion bodies. These inclusion bodies may be located in the cytosol or in the periplasm; the recovery of biologically active proteins from these inclusion bodies requires a denaturation/refolding process. Many recombinant proteins, including therapeutic proteins, are recovered from inclusion bodies. Alternatively, as will be clear to the skilled person, recombinant strains of bacteria that have been genetically modified so as to secrete a desired protein, and in particular an amino acid sequence, Nanobody or a polypeptide of the invention, can be used.

Thus, according to one non-limiting aspect of the invention, the amino acid sequence, Nanobody or polypeptide of the invention is an amino acid sequence, Nanobody or polypeptide that has been produced intracellularly and that has been isolated from the host cell, and in particular from a bacterial cell or from an inclusion body in a bacterial cell. According to another non-limiting aspect of the invention, the amino acid sequence, Nanobody or polypeptide of the invention is an amino acid sequence, Nanobody or polypeptide that has been produced extracellularly, and that has been isolated from the medium in which the host cell is cultivated.

Some preferred, but non-limiting promoters for use with these host cells include,

-   -   for expression in E. coli: lac promoter (and derivatives thereof         such as the lacUV5 promoter); arabinose promoter; left- (PL) and         rightward (PR) promoter of phage lambda; promoter of the trp         operon; hybrid lac/trp promoters (tac and trc); T7-promoter         (more specifically that of T7-phage gene 10) and other T-phage         promoters; promoter of the Tn10 tetracycline resistance gene;         engineered variants of the above promoters that include one or         more copies of an extraneous regulatory operator sequence;     -   for expression in S. cerevisiae: constitutive: ADH1 (alcohol         dehydrogenase 1), ENO (enolase), CYC1 (cytochrome c iso-1),         GAPDH (glyceraldehydes-3-phosphate dehydrogenase), PGK1         (phosphoglycerate kinase), PYK1 (pyruvate kinase); regulated:         GAL1,10,7 (galactose metabolic enzymes), ADH2 (alcohol         dehydrogenase 2), PHO5 (acid phosphatase), CUP1 (copper         metallothionein); heterologous: CaMV (cauliflower mosaic virus         35S promoter);     -   for expression in Pichia pastoris: the AOX1 promoter (alcohol         oxidase 1);     -   for expression in mammalian cells: human cytomegalovirus (hCMV)         immediate early enhancer/promoter; human cytomegalovirus (hCMV)         immediate early promoter variant that contains two tetracycline         operator sequences such that the promoter can be regulated by         the Tet repressor; Herpes Simplex Virus thymidine kinase (TK)         promoter; Rous Sarcoma Virus long terminal repeat (RSV LTR)         enhancer/promoter; elongation factor 1α (hEF-1α) promoter from         human, chimpanzee, mouse or rat; the SV40 early promoter; HIV-1         long terminal repeat promoter; β-actin promoter;

Some preferred, but non-limiting vectors for use with these host cells include:

-   -   vectors for expression in mammalian cells: pMAMneo (Clontech),         pcDNA3 (Invitrogen), pMC1neo (Stratagene), pSG5 (Stratagene),         EBO-pSV2-neo (ATCC 37593), pBPV-1 (8-2) (ATCC 37110),         pdBPV-MMTneo (342-12) (ATCC 37224), pRSVgpt (ATCC37199), pRSVneo         (ATCC37198), pSV2-dhfr (ATCC 37146), pUCTag (ATCC 37460) and         1ZD35 (ATCC 37565), as well as viral-based expression systems,         such as those based on adenovirus;     -   vectors for expression in bacterial cells: pET vectors (Novagen)         and pQE vectors (Qiagen);     -   vectors for expression in yeast or other fungal cells: pYES2         (Invitrogen) and Pichia expression vectors (Invitrogen);     -   vectors for expression in insect cells: pBlueBacII (Invitrogen)         and other baculovirus vectors     -   vectors for expression in plants or plant cells: for example         vectors based on cauliflower mosaic virus or tobacco mosaic         virus, suitable strains of Agrobacterium, or Ti-plasmid based         vectors.

Some preferred, but non-limiting secretory sequences for use with these host cells include:

-   -   for use in bacterial cells such as E. coli: PelB, Bla, OmpA,         OmpC, OmpF, OmpT, StII, PhoA, PhoE, MalE, Lpp, LamB, and the         like; TAT signal peptide, hemolysin C-terminal secretion signal;     -   for use in yeast: α-mating factor prepro-sequence, phosphatase         (pho1), invertase (Suc), etc.;     -   for use in mammalian cells: indigenous signal in case the target         protein is of eukaryotic origin; murine Ig κ-chain V-J2-C signal         peptide; etc.

Suitable techniques for transforming a host or host cell of the invention will be clear to the skilled person and may depend on the intended host cell/host organism and the genetic construct to be used. Reference is again made to the handbooks and patent applications mentioned above.

After transformation, a step for detecting and selecting those host cells or host organisms that have been successfully transformed with the nucleotide sequence/genetic construct of the invention may be performed. This may for instance be a selection step based on a selectable marker present in the genetic construct of the invention or a step involving the detection of the amino acid sequence of the invention, e.g. using specific antibodies.

The transformed host cell (which may be in the form or a stable cell line) or host organisms (which may be in the form of a stable mutant line or strain) form further aspects of the present invention.

Preferably, these host cells or host organisms are such that they express, or are (at least) capable of expressing (e.g. under suitable conditions), an amino acid sequence, Nanobody or polypeptide of the invention (and in case of a host organism: in at least one cell, part, tissue or organ thereof). The invention also includes further generations, progeny and/or offspring of the host cell or host organism of the invention, that may for instance be obtained by cell division or by sexual or asexual reproduction.

To produce/obtain expression of the amino acid sequences of the invention, the transformed host cell or transformed host organism may generally be kept, maintained and/or cultured under conditions such that the (desired) amino acid sequence, Nanobody or polypeptide of the invention is expressed/produced. Suitable conditions will be clear to the skilled person and will usually depend upon the host cell/host organism used, as well as on the regulatory elements that control the expression of the (relevant) nucleotide sequence of the invention. Again, reference is made to the handbooks and patent applications mentioned above in the paragraphs on the genetic constructs of the invention.

Generally, suitable conditions may include the use of a suitable medium, the presence of a suitable source of food and/or suitable nutrients, the use of a suitable temperature, and optionally the presence of a suitable inducing factor or compound (e.g. when the nucleotide sequences of the invention are under the control of an inducible promoter); all of which may be selected by the skilled person. Again, under such conditions, the amino acid sequences of the invention may be expressed in a constitutive manner, in a transient manner, or only when suitably induced.

It will also be clear to the skilled person that the amino acid sequence, Nanobody or polypeptide of the invention may (first) be generated in an immature form (as mentioned above), which may then be subjected to post-translational modification, depending on the host cell/host organism used. Also, the amino acid sequence, Nanobody or polypeptide of the invention may be glycosylated, again depending on the host cell/host organism used.

The amino acid sequence, Nanobody or polypeptide of the invention may then be isolated from the host cell/host organism and/or from the medium in which said host cell or host organism was cultivated, using protein isolation and/or purification techniques known per se, such as (preparative) chromatography and/or electrophoresis techniques, differential precipitation techniques, affinity techniques (e.g. using a specific, cleavable amino acid sequence fused with the amino acid sequence, Nanobody or polypeptide of the invention) and/or preparative immunological techniques (i.e. using antibodies against the amino acid sequence to be isolated).

Generally, for pharmaceutical use, the polypeptides of the invention may be formulated as a pharmaceutical preparation or compositions comprising at least one polypeptide of the invention and at least one pharmaceutically acceptable carrier, diluent or excipient and/or adjuvant, and optionally one or more further pharmaceutically active polypeptides and/or compounds. By means of non-limiting examples, such a formulation may be in a form suitable for oral administration, for parenteral administration (such as by intravenous, intramuscular or subcutaneous injection or intravenous infusion), for topical administration, for administration by inhalation, by a skin patch, by an implant, by a suppository, etc. Such suitable administration forms—which may be solid, semi-solid or liquid, depending on the manner of administration—as well as methods and carriers for use in the preparation thereof, will be clear to the skilled person, and are further described herein.

Thus, in a further aspect, the invention relates to a pharmaceutical composition that contains at least one amino acid of the invention, at least one Nanobody of the invention or at least one polypeptide of the invention and at least one suitable carrier, diluent or excipient (i.e. suitable for pharmaceutical use), and optionally one or more further active substances.

Generally, the amino acid sequences, Nanobodies and polypeptides of the invention can be formulated and administered in any suitable manner known per se, for which reference is for example made to the general background art cited above (and in particular to WO 04/041862, WO 04/041863, WO 04/041865. WO 04/041867 and WO 08/020079) as well as to the standard handbooks, such as Remington's Pharmaceutical Sciences, 18^(th) Ed., Mack Publishing Company, USA (1990), Remington, the Science and Practice of Pharmacy, 21st Edition, Lippincott Williams and Wilkins (2005) or the Handbook of Therapeutic Antibodies (S. Dubel, Ed.), Wiley, Weinheim, 2007 (see for example pages 252-255).

For example, the amino acid sequences, Nanobodies and polypeptides of the invention may be formulated and administered in any manner known per se for conventional antibodies and antibody fragments (including ScFv's and diabodies) and other pharmaceutically active proteins. Such formulations and methods for preparing the same will be clear to the skilled person, and for example include preparations suitable for parenteral administration (for example intravenous, intraperitoneal, subcutaneous, intramuscular, intraluminal, intra-arterial or intrathecal administration) or for topical (i.e. transdermal or intradermal) administration.

Preparations for parenteral administration may for example be sterile solutions, suspensions, dispersions or emulsions that are suitable for infusion or injection. Suitable carriers or diluents for such preparations for example include, without limitation, sterile water and aqueous buffers and solutions such as physiological phosphate-buffered saline, Ringer's solutions, dextrose solution, and Hank's solution; water oils; glycerol; ethanol; glycols such as propylene glycol or as well as mineral oils, animal oils and vegetable oils, for example peanut oil, soybean oil, as well as suitable mixtures thereof. Usually, aqueous solutions or suspensions will be preferred.

The amino acid sequences, Nanobodies and polypeptides of the invention can also be administered using gene therapy methods of delivery. See, e.g., U.S. Pat. No. 5,399,346, which is incorporated by reference in its entirety. Using a gene therapy method of delivery, primary cells transfected with the gene encoding an amino acid sequence, Nanobody or polypeptide of the invention can additionally be transfected with tissue specific promoters to target specific organs, tissue, grafts, tumors, or cells and can additionally be transfected with signal and stabilization sequences for subcellularly localized expression.

Thus, the amino acid sequences, Nanobodies and polypeptides of the invention may be systemically administered, e.g., orally, in combination with a pharmaceutically acceptable vehicle such as an inert diluent or an assimilable edible carrier. They may be enclosed in hard or soft shell gelatin capsules, may be compressed into tablets, or may be incorporated directly with the food of the patient's diet. For oral therapeutic administration, the amino acid sequences, Nanobodies and polypeptides of the invention may be combined with one or more excipients and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. Such compositions and preparations should contain at least 0.1% of the amino acid sequence, Nanobody or polypeptide of the invention. Their percentage in the compositions and preparations may, of course, be varied and may conveniently be between about 2 to about 60% of the weight of a given unit dosage form. The amount of the amino acid sequence, Nanobody or polypeptide of the invention in such therapeutically useful compositions is such that an effective dosage level will be obtained.

The tablets, troches, pills, capsules, and the like may also contain the following: binders such as gum tragacanth, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, fructose, lactose or aspartame or a flavoring agent such as peppermint, oil of wintergreen, or cherry flavoring may be added. When the unit dosage form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier, such as a vegetable oil or a polyethylene glycol. Various other materials may be present as coatings or to otherwise modify the physical form of the solid unit dosage form. For instance, tablets, pills, or capsules may be coated with gelatin, wax, shellac or sugar and the like. A syrup or elixir may contain the amino acid sequences, Nanobodies and polypeptides of the invention, sucrose or fructose as a sweetening agent, methyl and propylparabens as preservatives, a dye and flavoring such as cherry or orange flavor. Of course, any material used in preparing any unit dosage form should be pharmaceutically acceptable and substantially non-toxic in the amounts employed. In addition, the amino acid sequences, Nanobodies and polypeptides of the invention may be incorporated into sustained-release preparations and devices.

Preparations and formulations for oral administration may also be provided with an enteric coating that will allow the constructs of the invention to resist the gastric environment and pass into the intestines. More generally, preparations and formulations for oral administration may be suitably formulated for delivery into any desired part of the gastrointestinal tract. In addition, suitable suppositories may be used for delivery into the gastrointestinal tract.

The amino acid sequences, Nanobodies and polypeptides of the invention may also be administered intravenously or intraperitoneally by infusion or injection. Solutions of the amino acid sequences, Nanobodies and polypeptides of the invention or their salts can be prepared in water, optionally mixed with a nontoxic surfactant. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, triacetin, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms.

The pharmaceutical dosage forms suitable for injection or infusion can include sterile aqueous solutions or dispersions or sterile powders comprising the active ingredient which are adapted for the extemporaneous preparation of sterile injectable or infusible solutions or dispersions, optionally encapsulated in liposomes. In all cases, the ultimate dosage form must be sterile, fluid and stable under the conditions of manufacture and storage. The liquid carrier or vehicle can be a solvent or liquid dispersion medium comprising, for example, water, ethanol, a polyol (for example, glycerol, propylene glycol, liquid polyethylene glycols, and the like), vegetable oils, nontoxic glyceryl esters, and suitable mixtures thereof. The proper fluidity can be maintained, for example, by the formation of liposomes, by the maintenance of the required particle size in the case of dispersions or by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars, buffers or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin.

Sterile injectable solutions are prepared by incorporating the amino acid sequences, Nanobodies and polypeptides of the invention in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filter sterilization. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and the freeze drying techniques, which yield a powder of the active ingredient plus any additional desired ingredient present in the previously sterile-filtered solutions.

For topical administration, the amino acid sequences, Nanobodies and polypeptides of the invention may be applied in pure form, i.e., when they are liquids. However, it will generally be desirable to administer them to the skin as compositions or formulations, in combination with a dermatologically acceptable carrier, which may be a solid or a liquid.

Useful solid carriers include finely divided solids such as talc, clay, microcrystalline cellulose, silica, alumina and the like. Useful liquid carriers include water, hydroxyalkyls or glycols or water-alcohol/glycol blends, in which the amino acid sequences, Nanobodies and polypeptides of the invention can be dissolved or dispersed at effective levels, optionally with the aid of non-toxic surfactants. Adjuvants such as fragrances and additional antimicrobial agents can be added to optimize the properties for a given use. The resultant liquid compositions can be applied from absorbent pads, used to impregnate bandages and other dressings, or sprayed onto the affected area using pump-type or aerosol sprayers.

Thickeners such as synthetic polymers, fatty acids, fatty acid salts and esters, fatty alcohols, modified celluloses or modified mineral materials can also be employed with liquid carriers to form spreadable pastes, gels, ointments, soaps, and the like, for application directly to the skin of the user.

Examples of useful dermatological compositions which can be used to deliver the amino acid sequences, Nanobodies and polypeptides of the invention to the skin are known to the art; for example, see Jacquet et al. (U.S. Pat. No. 4,608,392), Geria (U.S. Pat. No. 4,992,478), Smith et al. (U.S. Pat. No. 4,559,157) and Wortzman (U.S. Pat. No. 4,820,508).

Useful dosages of the amino acid sequences, Nanobodies and polypeptides of the invention can be determined by comparing their in vitro activity, and in vivo activity in animal models. Methods for the extrapolation of effective dosages in mice, and other animals, to humans are known to the art; for example, see U.S. Pat. No. 4,938,949.

Generally, the concentration of the amino acid sequences, Nanobodies and polypeptides of the invention in a liquid composition, such as a lotion, will be from about 0.1-25 wt-%, preferably from about 0.5-10 wt-%. The concentration in a semi-solid or solid composition such as a gel or a powder will be about 0.1-5 wt-%, preferably about 0.5-2.5 wt-%.

The amount of the amino acid sequences, Nanobodies and polypeptides of the invention required for use in treatment will vary not only with the particular amino acid sequence, Nanobody or polypeptide selected but also with the route of administration, the nature of the condition being treated and the age and condition of the patient and will be ultimately at the discretion of the attendant physician or clinician. Also the dosage of the amino acid sequences, Nanobodies and polypeptides of the invention varies depending on the target cell, tumor, tissue, graft, or organ.

The desired dose may conveniently be presented in a single dose or as divided doses administered at appropriate intervals, for example, as two, three, four or more sub-doses per day. The sub-dose itself may be further divided, e.g., into a number of discrete loosely spaced administrations; such as multiple inhalations from an insufflator or by application of a plurality of drops into the eye.

An administration regimen could include long-term, daily treatment. By “long-term” is meant at least two weeks and preferably, several weeks, months, or years of duration. Necessary modifications in this dosage range may be determined by one of ordinary skill in the art using only routine experimentation given the teachings herein. See Remington's Pharmaceutical Sciences (Martin, E. W., ed. 4), Mack Publishing Co., Easton, Pa. The dosage can also be adjusted by the individual physician in the event of any complication.

In another aspect, the invention relates to a method for the prevention and/or treatment of at least one viral and/or bacteria induced disease and/or disorders, said method comprising administering, to a subject in need thereof, a pharmaceutically active amount of an amino acid sequence of the invention, of a Nanobody of the invention, of a polypeptide of the invention, and/or of a pharmaceutical composition comprising the same.

In the context of the present invention, the term “prevention and/or treatment” not only comprises preventing and/or treating the disease, but also generally comprises preventing the onset of the disease, slowing or reversing the progress of disease, preventing or slowing the onset of one or more symptoms associated with the disease, reducing and/or alleviating one or more symptoms associated with the disease, reducing the severity and/or the duration of the disease and/or of any symptoms associated therewith and/or preventing a further increase in the severity of the disease and/or of any symptoms associated therewith, preventing, reducing or reversing any physiological damage caused by the disease, and generally any pharmacological action that is beneficial to the patient being treated.

The subject to be treated may be any warm-blooded animal, but is in particular a mammal, and more in particular a human being. As will be clear to the skilled person, the subject to be treated will in particular be a person suffering from, or at risk of, the diseases and disorders mentioned herein.

The invention relates to a method for the prevention and/or treatment of at least one disease or disorder that is associated with Targets of the invention, with its biological or pharmacological activity, and/or with the biological pathways or signalling in which Targets of the invention is involved, said method comprising administering, to a subject in need thereof, a pharmaceutically active amount of an amino acid sequence of the invention, of a Nanobody of the invention, of a polypeptide of the invention, and/or of a pharmaceutical composition comprising the same. In particular, the invention relates to a method for the prevention and/or treatment of at least one disease or disorder that can be treated by modulating Targets of the invention, its biological or pharmacological activity, and/or the biological pathways or signalling in which Targets of the invention is involved, said method comprising administering, to a subject in need thereof, a pharmaceutically active amount of an amino acid sequence of the invention, of a Nanobody of the invention, of a polypeptide of the invention, and/or of a pharmaceutical composition comprising the same. In particular, said pharmaceutically effective amount may be an amount that is sufficient to modulate Targets of the invention, its biological or pharmacological activity, and/or the biological pathways or signalling in which Targets of the invention is involved; and/or an amount that provides a level of the amino acid sequence of the invention, of a Nanobody of the invention, of a polypeptide of the invention in the circulation that is sufficient to modulate Targets of the invention, its biological or pharmacological activity, and/or the biological pathways or signalling in which Targets of the invention is involved.

The invention furthermore relates to a method for the prevention and/or treatment of at least one disease or disorder that can be prevented and/or treated by administering an amino acid sequence of the invention, a Nanobody of the invention or a polypeptide of the invention to a patient, said method comprising administering, to a subject in need thereof, a pharmaceutically active amount of an amino acid sequence of the invention, of a Nanobody of the invention, of a polypeptide of the invention, and/or of a pharmaceutical composition comprising the same.

More in particular, the invention relates to a method for the prevention and/or treatment of at least one disease or disorder chosen from the group consisting of the diseases and disorders listed herein, said method comprising administering, to a subject in need thereof, a pharmaceutically active amount of an amino acid sequence of the invention, of a Nanobody of the invention, of a polypeptide of the invention, and/or of a pharmaceutical composition comprising the same.

In another aspect, the invention relates to a method for immunotherapy, and in particular for passive immunotherapy, which method comprises administering, to a subject suffering from or at risk of the diseases and disorders mentioned herein, a pharmaceutically active amount of an amino acid sequence of the invention, of a Nanobody of the invention, of a polypeptide of the invention, and/or of a pharmaceutical composition comprising the same.

In the above methods, the amino acid sequences, Nanobodies and/or polypeptides of the invention and/or the compositions comprising the same can be administered in any suitable manner, depending on the specific pharmaceutical formulation or composition to be used. Thus, the amino acid sequences, Nanobodies and/or polypeptides of the invention and/or the compositions comprising the same can for example be administered orally, intraperitoneally (e.g. intravenously, subcutaneously, intramuscularly, or via any other route of administration that circumvents the gastrointestinal tract), intranasally, transdermally, topically, by means of a suppository, by inhalation, again depending on the specific pharmaceutical formulation or composition to be used. The clinician will be able to select a suitable route of administration and a suitable pharmaceutical formulation or composition to be used in such administration, depending on the disease or disorder to be prevented or treated and other factors well known to the clinician.

The amino acid sequences, Nanobodies and/or polypeptides of the invention and/or the compositions comprising the same are administered according to a regime of treatment that is suitable for preventing and/or treating the disease or disorder to be prevented or treated. The clinician will generally be able to determine a suitable treatment regimen, depending on factors such as the disease or disorder to be prevented or treated, the severity of the disease to be treated and/or the severity of the symptoms thereof, the specific amino acid sequence, Nanobody or polypeptide of the invention to be used, the specific route of administration and pharmaceutical formulation or composition to be used, the age, gender, weight, diet, general condition of the patient, and similar factors well known to the clinician.

Generally, the treatment regimen will comprise the administration of one or more amino acid sequences, Nanobodies and/or polypeptides of the invention, or of one or more compositions comprising the same, in one or more pharmaceutically effective amounts or doses. The specific amount(s) or doses to administered can be determined by the clinician, again based on the factors cited above.

Generally, for the prevention and/or treatment of the diseases and disorders mentioned herein and depending on the specific disease or disorder to be treated, the potency of the specific amino acid sequence, Nanobody and polypeptide of the invention to be used, the specific route of administration and the specific pharmaceutical formulation or composition used, the amino acid sequences, Nanobodies and polypeptides of the invention will generally be administered in an amount between 1 gram and 0.01 microgram per kg body weight per day, preferably between 0.1 gram and 0.1 microgram per kg body weight per day, such as about 1, 10, 100 or 1000 microgram per kg body weight per day, either continuously (e.g. by infusion), as a single daily dose or as multiple divided doses during the day. The clinician will generally be able to determine a suitable daily dose, depending on the factors mentioned herein. It will also be clear that in specific cases, the clinician may choose to deviate from these amounts, for example on the basis of the factors cited above and his expert judgment. Generally, some guidance on the amounts to be administered can be obtained from the amounts usually administered for comparable conventional antibodies or antibody fragments against the same target administered via essentially the same route, taking into account however differences in affinity/avidity, efficacy, biodistribution, half-life and similar factors well known to the skilled person.

Usually, in the above method, a single amino acid sequence, Nanobody or polypeptide of the invention will be used. It is however within the scope of the invention to use two or more amino acid sequences, Nanobodies and/or polypeptides of the invention in combination.

The Nanobodies, amino acid sequences and polypeptides of the invention may also be used in combination with one or more further pharmaceutically active compounds or principles, i.e. as a combined treatment regimen, which may or may not lead to a synergistic effect. Again, the clinician will be able to select such further compounds or principles, as well as a suitable combined treatment regimen, based on the factors cited above and his expert judgement.

In particular, the amino acid sequences, Nanobodies and polypeptides of the invention may be used in combination with other pharmaceutically active compounds or principles (such as e.g. a virus blocker) that are or can be used for the prevention and/or treatment of the diseases and disorders cited herein, as a result of which a synergistic effect may or may not be obtained. Examples of such compounds and principles, as well as routes, methods and pharmaceutical formulations or compositions for administering them will be clear to the clinician.

When two or more substances or principles are to be used as part of a combined treatment regimen, they can be administered via the same route of administration or via different routes of administration, at essentially the same time or at different times (e.g. essentially simultaneously, consecutively, or according to an alternating regime). When the substances or principles are to be administered simultaneously via the same route of administration, they may be administered as different pharmaceutical formulations or compositions or part of a combined pharmaceutical formulation or composition, as will be clear to the skilled person.

Also, when two or more active substances or principles are to be used as part of a combined treatment regimen, each of the substances or principles may be administered in the same amount and according to the same regimen as used when the compound or principle is used on its own, and such combined use may or may not lead to a synergistic effect. However, when the combined use of the two or more active substances or principles leads to a synergistic effect, it may also be possible to reduce the amount of one, more or all of the substances or principles to be administered, while still achieving the desired therapeutic action. This may for example be useful for avoiding, limiting or reducing any unwanted side-effects that are associated with the use of one or more of the substances or principles when they are used in their usual amounts, while still obtaining the desired pharmaceutical or therapeutic effect.

The effectiveness of the treatment regimen used according to the invention may be determined and/or followed in any manner known per se for the disease or disorder involved, as will be clear to the clinician. The clinician will also be able, where appropriate and on a case-by-case basis, to change or modify a particular treatment regimen, so as to achieve the desired therapeutic effect, to avoid, limit or reduce unwanted side-effects, and/or to achieve an appropriate balance between achieving the desired therapeutic effect on the one hand and avoiding, limiting or reducing undesired side effects on the other hand.

Generally, the treatment regimen will be followed until the desired therapeutic effect is achieved and/or for as long as the desired therapeutic effect is to be maintained. Again, this can be determined by the clinician.

In another aspect, the invention relates to the use of an amino acid sequence, Nanobody or polypeptide of the invention in the preparation of a pharmaceutical composition for prevention and/or treatment of at least one viral and/or bacteria induced disease and/or disorder; and/or for use in one or more of the methods of treatment mentioned herein.

The subject to be treated may be any warm-blooded animal, but is in particular a mammal, and more in particular a human being. As will be clear to the skilled person, the subject to be treated will in particular be a person suffering from, or at risk of, the diseases and disorders mentioned herein.

The invention also relates to the use of an amino acid sequence, Nanobody or polypeptide of the invention in the preparation of a pharmaceutical composition for the prevention and/or treatment of at least one disease or disorder that can be prevented and/or treated by administering an amino acid sequence, Nanobody or polypeptide of the invention to a patient.

More in particular, the invention relates to the use of an amino acid sequence, Nanobody or polypeptide of the invention in the preparation of a pharmaceutical composition for the prevention and/or treatment of viral and/or bacteria induced diseases and disorders, and in particular for the prevention and treatment of one or more of the diseases and disorders listed herein.

Again, in such a pharmaceutical composition, the one or more amino acid sequences, Nanobodies or polypeptides of the invention may also be suitably combined with one or more other active principles, such as those mentioned herein.

Finally, although the use of the Nanobodies of the invention (as defined herein) and of the polypeptides of the invention is much preferred, it will be clear that on the basis of the description herein, the skilled person will also be able to design and/or generate, in an analogous manner, other amino acid sequences and in particular (single) domain antibodies against Targets of the invention, as well as polypeptides comprising such (single) domain antibodies.

For example, it will also be clear to the skilled person that it may be possible to “graft” one or more of the CDR's mentioned above for the Nanobodies of the invention onto such (single) domain antibodies or other protein scaffolds, including but not limited to human scaffolds or non-immunoglobulin scaffolds. Suitable scaffolds and techniques for such CDR grafting will be clear to the skilled person and are well known in the art, see for example U.S. Pat. No. 7,180,370, WO 01/27160, EP 0 605 522, EP 0 460 167, U.S. Pat. No. 7,054,297, Nicaise et al., Protein Science (2004), 13:1882-1891; Ewert et al., Methods, 2004 October; 34(2):184-199; Kettleborough et al., Protein Eng. 1991 October; 4(7): 773-783; O'Brien and Jones, Methods Mol. Biol. 2003:207:81-100; Skerra, J. Mot. Recognit. 2000:13:167-187, and Saerens et al., J. Mol. Biol. 2005 Sep. 23; 352(3):597-607, and the further references cited therein. For example, techniques known per se for grafting mouse or rat CDR's onto human frameworks and scaffolds can be used in an analogous manner to provide chimeric proteins comprising one or more of the CDR's of the Nanobodies of the invention and one or more human framework regions or sequences.

It should also be noted that, when the Nanobodies of the inventions contain one or more other CDR sequences than the preferred. CDR sequences mentioned above, these CDR sequences can be obtained in any manner known per se, for example from Nanobodies (preferred), V_(H) domains from conventional antibodies (and in particular from human antibodies), heavy chain antibodies, conventional 4-chain antibodies (such as conventional human 4-chain antibodies) or other immunoglobulin sequences directed against Targets of the invention. Such immunoglobulin sequences directed against Targets of the invention can be generated in any manner known per se, as will be clear to the skilled person, i.e. by immunization with Targets of the invention or by screening a suitable library of immunoglobulin sequences with Targets of the invention, or any suitable combination thereof. Optionally, this may be followed by techniques such as random or site-directed mutagenesis and/or other techniques for affinity maturation known per se. Suitable techniques for generating such immunoglobulin sequences will be clear to the skilled person, and for example include the screening techniques reviewed by Hoogenboom, Nature Biotechnology, 23, 9, 1105-1116 (2005) Other techniques for generating immunoglobulins against a specified target include for example the Nanoclone technology (as for example described in the published US patent application 2006-0211088), so-called SLAM technology (as for example described in the European patent application 0 542 810), the use of transgenic mice expressing human immunoglobulins or the well-known hybridoma techniques (see for example Larrick et al, Biotechnology, Vol. 7, 1989, p. 934). All these techniques can be used to generate immunoglobulins against Targets of the invention, and the CDR's of such immunoglobulins can be used in the Nanobodies of the invention, i.e. as outlined above. For example, the sequence of such a CDR can be determined, synthesized and/or isolated, and inserted into the sequence of a Nanobody of the invention (e.g. so as to replace the corresponding native CDR), all using techniques known per se such as those described herein, or Nanobodies of the invention containing such CDR's (or nucleic acids encoding the same) can be synthesized de novo, again using the techniques mentioned herein.

Further uses of the amino acid sequences, Nanobodies, polypeptides, nucleic acids, genetic constructs and hosts and host cells of the invention will be clear to the skilled person based on the disclosure herein. For example, and without limitation, the amino acid sequences of the invention can be linked to a suitable carrier or solid support so as to provide a medium than can be used in a manner known per se to purify Targets of the invention from compositions and preparations comprising the same. Derivatives of the amino acid sequences of the invention that comprise a suitable detectable label can also be used as markers to determine (qualitatively or quantitatively) the presence of Targets of the invention in a composition or preparation or as a marker to selectively detect the presence of Targets of the invention on the surface of a cell or tissue (for example, in combination with suitable cell sorting techniques).

The invention will now be further described by means of the following non-limiting aspects and experimental part:

Preferred Aspects:

-   Aspect A-1: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention and that inhibits entry of a virus such as     e.g. HIV, HCV, adenoviruses, hantavirus, herpesvirus, echo-virus 1     and others into cells. -   Aspect A-2: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention and wherein the IC50 in the HIV-1 infection     assays is equal or below 100 nM, preferably 50 nM, more preferably     10 nM, even more preferably 1 nM. -   Aspect A-3: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention and that has an antiviral activity     (expressed as IC50 measured in the HIV-1 infection assay) equal or     below 100 nM, preferably 50 nM, more preferably 10 nM, even more     preferably 1 nM. -   Aspect A-4: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of hCD4,     hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin,     human beta1 integrin, human alpha2 integrin, hCD81, hSR-SI,     hClaudin-1, hClaudin-6 and hClaudin-9 and that inhibits entry of HIV     into cells. -   Aspect A-5: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of hCD4,     hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin,     human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI,     hClaudin-1, hClaudin-6 and hClaudin-9 and wherein the IC50 in the     HIV-1 infection assays is equal or below 100 nM, preferably 50 nM,     more preferably 10 nM, even more preferably 1 nM. -   Aspect A-6: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of hCD4,     hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin,     human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI,     hClaudin-1, hClaudin-6 and hClaudin-9 and that has an antiviral     activity (expressed as IC50 measured in the HIV-1 infection assay)     equal or below 100 nM, preferably 50 nM, more preferably 10 nM, even     more preferably 1 nM. -   Aspect A-7: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of amino     acid sequences with SEQ IDs: 254, 268 to 279 and that inhibits entry     of HIV into cells. -   Aspect A-8: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of amino     acid sequences with SEQ IDs: 254, 268 to 279 and wherein the IC50 in     the HIV-1 infection assays is equal or below 100 nM, preferably 50     nM, more preferably 10 nM, even more preferably 1 nM. -   Aspect A-9: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of amino     acid sequences with SEQ IDs: 254, 268 to 279 and that has an     antiviral activity (expressed as IC50 measured in the HIV-1     infection assay) equal or below 100 nM, preferably 50 nM, more     preferably 10 nM, even more preferably 1 nM. -   Aspect A-10: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to to hCXCR4 (SEQ     ID NO: 254) and that inhibits entry of HIV into cells. -   Aspect A-11: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to to hCXCR4 (SEQ     ID NO: 254) and wherein the IC50 in the HIV-1 infection assays is     equal or below 100 nM, preferably 50 nM, more preferably 10 nM, even     more preferably 1 nM. -   Aspect A-12: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to to hCXCR4 (SEQ     ID NO: 254) and that has an antiviral activity (expressed as IC50     measured in the HIV-1 infection assay) equal or below 100 nM,     preferably 50 nM, more preferably 10 nM, even more preferably 1 nM. -   Aspect A-13: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention, e.g. selected from the group consisting of     hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3     integrin, human beta1 integrin, human alpha2 integrin, hCD81,     hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9. -   Aspect A-14: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to at least one     of the Targets of the invention, e.g. CXCR4, CXCR7 or CD4. -   Aspect A-15: Amino acid sequence, e.g. single variable domain     according to aspect A-14, wherein the member of CXCR4 is human     CXCR4. -   Aspect A-16: Amino acid sequence, e.g. single variable domain     according to aspect A-14, wherein the member of CD4 is human CD4. -   Aspect A-17: Amino acid sequence, e.g. single variable domain     according to aspect A-14, wherein the member of CXCR7 is human     CXCR7. -   Aspect A-18: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to one of the     Targets of the invention, e.g. selected from the group consisting of     hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3     integrin, human beta1 integrin, human alpha2 integrin, hCD81,     hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9 and inhibits and/or     blocks binding of the Target of the invention to its ligand. -   Aspect A-19: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to hCD4 and     inhibits and/or blocks binding of gp120 to hCD4. -   Aspect A-20: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that specifically binds to hCXCR4 and     inhibits and/or blocks binding of CXCL12 to hCXCR4. -   Aspect A-21: Amino acid sequence, e.g. single variable domain, that     is directed against and/or that a) specifically binds to one of the     Targets of the invention; and b) fully inhibits ligand-dependent     activation of one of the Targets of the invention, e.g. selected     from the group consisting of hCD4, hCXCR4, hCCR5, hTLR4, human     alphaV integrin, human beta3 integrin, human beta1 integrin, human     alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and     hClaudin-9, wherein the ligand is present in a concentration of 100     nM or less, more preferably 30 nM or less; and c) provides no     activation of one of the Targets of the invention. -   Aspect A-22: Amino acid sequence, e.g. single variable domain     according to aspect A-1 to A16, that is in essentially isolated     form. -   Aspect A-23: Amino acid sequence, e.g. single variable domain     according to aspect A-1 or A-17, for administration to a subject,     wherein said amino acid sequence does not naturally occur in said     subject. -   Aspect A-24: Amino acid sequence, e.g. single variable domain that     can specifically bind to one of the Targets of the invention, e.g.     selected from the group consisting of hCD4, hCXCR4, hCCR5, hTLR4,     human alphaV integrin, human beta3 integrin, human beta1 integrin,     human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and     hClaudin-9 with a dissociation constant (K_(D)) of 10⁻⁵ to 10⁻¹²     moles/litre or less, and preferably 10⁻⁷ to 10⁻¹² moles/litre or     less and more preferably 10⁻⁸ to 10⁻¹² moles/litre. Such an amino     acid sequence may in particular be an amino acid sequence according     to any of the preceding aspects. -   Aspect A-25: Amino acid sequence, e.g. single variable domain that     can specifically bind to one of the Targets of the invention, e.g.     selected from the group consisting of hCD4, hCXCR4, hCCR5, hTLR4,     human alphaV integrin, human beta3 integrin, human beta1 integrin,     human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and     hClaudin-9 with a rate of association (k_(on)-rate) of between 10²     M⁻¹s⁻¹ to about 10⁷ M⁻¹s⁻¹, preferably between 10³ M⁻¹s⁻¹ and 10⁷     M⁻¹s⁻¹, more preferably between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, such as     between 10⁵ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹. Such an amino acid sequence may     in particular be an amino acid sequence according to any of the     preceding aspects. -   Aspect A-26: Amino acid sequence, e.g. single variable domain that     can specifically bind to one of the Targets of the invention, e.g.     selected from the group consisting of hCD4, hCXCR4, hCCR5, hTLR4,     human alphaV integrin, human beta3 integrin, human beta1 integrin,     human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and     hClaudin-9 with a rate of dissociation (k_(off) rate) between 1 s⁻¹     and 10⁻⁶ s⁻¹, preferably between 10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more     preferably between 10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as between 10⁻⁴ s⁻¹     and 10⁻⁶ s⁻¹. Such an amino acid sequence may in particular be an     amino acid sequence according to any of the preceding aspects. -   Aspect A-27: Amino acid sequence, e.g. single variable domain that     can specifically bind to one of the Targets of the invention, e.g.     selected from the group consisting of hCD4, hCXCR4, hCCR5, hTLR4,     human alphaV integrin, human beta3 integrin, human beta1 integrin,     human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and     hClaudin-9 with an affinity less than 500 nM, preferably less than     200 nM, more preferably less than 10 nM, such as less than 500 pM.     Such an amino acid sequence may in particular be an amino acid     sequence according to any of the preceding aspects. -   Aspect A-28: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that is a naturally     occurring amino acid sequence (from any suitable species) or a     synthetic or semi-synthetic amino acid sequence. -   Aspect A-29: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that comprises an     immunoglobulin fold or that under suitable conditions is capable of     forming an immunoglobulin fold. -   Aspect A-30: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of 4 framework regions (FR1 to FR4 respectively) and 3     complementarity determining regions (CDR1 to CDR3 respectively). -   Aspect A-31: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that is an immunoglobulin     sequence. -   Aspect A-32: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that is a naturally     occurring immunoglobulin sequence (from any suitable species) or a     synthetic or semi-synthetic immunoglobulin sequence. -   Aspect A-33: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects that is a humanized     immunoglobulin sequence, a camelized immunoglobulin sequence or an     immunoglobulin sequence that has been obtained by techniques such as     affinity maturation. -   Aspect A-34: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of a light chain variable domain sequence (e.g. a VL-sequence); or     of a heavy chain variable domain sequence (e.g. a VH-sequence). -   Aspect A-35: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of a heavy chain variable domain sequence that is derived from a     conventional four-chain antibody or that essentially consist of a     heavy chain variable domain sequence that is derived from heavy     chain antibody. -   Aspect A-36: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of a domain antibody (or an amino acid sequence that is suitable for     use as a domain antibody), of a single domain antibody (or an amino     acid sequence that is suitable for use as a single domain antibody),     of a “dAb” (or an amino acid sequence that is suitable for use as a     dAb) or of a Nanobody (including but not limited to a VHH sequence). -   Aspect A-37: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of a Nanobody. -   Aspect A-38: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of a Nanobody that     -   i) has at least 80% amino acid identity with at least one of the         An amino acid sequences of SEQ ID NO's: 1 to 22, in which for         the purposes of determining the degree of amino acid identity,         the amino acid residues that form the CDR sequences are         disregarded;     -   and in which:     -   ii) preferably one or more of the amino acid residues at         positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according         to the Kabat numbering are chosen from the Hallmark residues         mentioned in Table A-3. -   Aspect A-39: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of a polypeptide that     -   i) has at least 80% amino acid identity with at least one of the         amino acid sequences of SEQ ID NO's: 238 to 253, more preferably         238 to 239 and one of the amino acid sequences of SEQ ID NO's:         308 to 311, more preferably 311, in which for the purposes of         determining the degree of amino acid identity, the amino acid         residues that form the CDR sequences are disregarded;     -   and in which:     -   ii) preferably one or more of the amino acid residues at         positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according         to the Kabat numbering are chosen from the Hallmark residues         mentioned in Table A-3. -   Aspect A-40: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of a Nanobody that     -   i) has at least 80% amino acid identity with at least one of the         amino acid sequences of SEQ ID NO's: 238 to 253, more preferably         238 to 239 and one of the amino acid sequences of SEQ ID NO's:         308 to 311, more preferably 311, in which for the purposes of         determining the degree of amino acid identity, the amino acid         residues that form the CDR sequences are disregarded;     -   and in which:     -   ii) preferably one or more of the amino acid residues at         positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according         to the Kabat numbering are chosen from the Hallmark residues         mentioned in Table B-2. -   Aspect A-41: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that essentially consists     of a humanized Nanobody. -   Aspect A-42: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that in addition to the     at least one binding site for binding against one of the Targets of     the invention, e.g. selected from the group consisting of hCD4,     hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin,     human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI,     hClaudin-1, hClaudin-6 and hClaudin-9, contains one or more further     binding sites for binding against other antigens, proteins or     targets. -   Aspect B-1: Amino acid sequence, e.g. single variable domain that is     directed against and/or that can specifically bind hCXCR4, and that     comprises one or more stretches of amino acid residues chosen from     the group consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more         preferably 142 to 143;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 142 to 157, more preferably 142 to 143;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 142 to 157, more preferably 142 to 143;     -   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more         preferably 174 to 175;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 174 to 189, more preferably 174 to 175;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 174 to 189, more preferably 174 to 175;     -   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more         preferably 206 to 207;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 206 to 221, more preferably 206 to 207;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 206 to 221, more preferably 206 to 207;     -   or any suitable combination thereof.         Such an amino acid sequence may in particular be an amino acid         sequence according to any of the aspects A-1 to A-42. -   Aspect B-2: Amino acid sequence, e.g. single variable domain     according to aspect B-1, in which at least one of said stretches of     amino acid residues forms part of the antigen binding site for     binding against hCXCR4. -   Aspect B-3: Amino acid sequence, e.g. single variable domain that is     directed against and/or that can specifically bind hCXCR4 and that     comprises two or more stretches of amino acid residues chosen from     the group consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more         preferably 142 to 143;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 142 to 157, more preferably 142 to 143;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 142 to 157, more preferably 142 to 143;     -   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more         preferably 174 to 175;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 174 to 189, more preferably 174 to 175;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 174 to 189, more preferably 174 to 175;     -   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more         preferably 206 to 207;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ         NO's: 206 to 221, more preferably 206 to 207;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 206 to 221, more preferably 206 to 207;     -   such that (i) when the first stretch of amino acid residues         corresponds to one of the amino acid sequences according to         a), b) or c), the second stretch of amino acid residues         corresponds to one of the amino acid sequences according to d),         e), f), g), h) or i); (ii) when the first stretch of amino acid         residues corresponds to one of the amino acid sequences         according to d), e) or f), the second stretch of amino acid         residues corresponds to one of the amino acid sequences         according to a), b), c), g), h) or i); or (iii) when the first         stretch of amino acid residues corresponds to one of the amino         acid sequences according to g), h) or i), the second stretch of         amino acid residues corresponds to one of the amino acid         sequences according to a), b), c), d), e) or f).         Such an amino acid sequence may in particular be an amino acid         sequence according to any of the aspects A-1 to A-42, B-1 or         B-2. -   Aspect B-4: Amino acid sequence, e.g. single variable domain     according to aspect B-3, in which the at least two stretches of     amino acid residues forms part of the antigen binding site for     binding against hCXCR4. -   Aspect B-5: Amino acid sequence, e.g. single variable domain that is     directed against and/or that can specifically hind hCXCR4 and that     comprises three or more stretches of amino acid residues, in which     the first stretch of amino acid residues is chosen from the group     consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more         preferably 142 to 143;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 142 to 157, more preferably 142 to 143;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 142 to 157, more preferably 142 to 143;     -   the second stretch of amino acid residues is chosen from the         group consisting of:     -   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more         preferably 174 to 175;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 174 to 189, more preferably 174 to 175;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 174 to 189, more preferably 174 to 175;     -   and the third stretch of amino acid residues is chosen from the         group consisting of:     -   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more         preferably 206 to 207;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 206 to 221, more preferably 206 to 207;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 206 to 221, more preferably 206 to 207.         Such an amino acid sequence may in particular be an amino acid         sequence according to any of the aspects A-1 to A-42 and/or B-1         to B-4. -   Aspect B-6: Amino acid sequence, e.g. single variable domain     according to aspect B-5, in which the at least three stretches of     amino acid residues forms part of the antigen binding site for     binding against hCXCR4. -   Aspect B-7: Amino acid sequence, e.g. single variable domain that is     directed against and/or that can specifically bind hCXCR4 in which     the CDR sequences of said amino acid sequence have at least 70%     amino acid identity, preferably at least 80% amino acid identity,     more preferably at least 90% amino acid identity, such as 95% amino     acid identity or more or even essentially 100% amino acid identity     with the CDR sequences of at least one of the amino acid sequences     of SEQ ID NO's: 238 to 253, preferably 238 to 239. Such an amino     acid sequence may in particular be an amino acid sequence according     to any of the aspects A-1 to A-42 and/or B-1 to B-6. -   Aspect B-8: Amino acid sequence, e.g. single variable domain that is     directed against and/or that can specifically bind hCXCR4, wherein     the amino acid sequence is selected from the group consisting of a)     amino acid sequences with SEQ ID NO'S: 238 to 253, more preferably     238 to 239; and b) amino acid sequences with SEQ ID NO'S: 238 to     253, more preferably 238 to 239, wherein up to 10 amino acid     residues are replaced by naturally occurring amino acids and wherein     said replaced amino acids are located within the framework regions. -   Aspect B-9: Amino acid sequence, e.g. single variable domain that is     directed against and/or that can specifically bind hCXCR4, wherein     the amino acid sequence is selected from the group consisting of a)     amino acid sequences with SEQ ID NO'S: 238 to 253, more preferably     238 to 239; and b) amino acid sequences with SEQ ID NO'S: 238 to     253, more preferably 238 to 239, wherein up to 8 amino acid residues     are replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions. -   Aspect B-10: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCXCR4,     wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO'S: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with SEQ ID     NO: 238 to 253, more preferably 238 to 239, wherein up to 5 amino     acid residues are replaced by naturally occurring amino acids and     wherein said replaced amino acids are located within the framework     regions. -   Aspect B-11: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCXCR4,     wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO'S: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with SEQ ID     NO'S: 238 to 253, more preferably 238 to 239, wherein up to 3 amino     acid residues are replaced by naturally occurring amino acids and     wherein said replaced amino acids are located within the framework     regions. -   Aspect C-1: Amino acid sequence, e.g. single variable domain that is     directed against hCXCR4 and that cross-blocks the binding of at     least one of the amino acid sequences of SEQ ID NO's: 238 to 253,     preferably 238 to 239 to hCXCR4. Such an amino acid sequence may in     particular be an amino acid sequence according to any of the aspects     A-1 to A-42 and/or according to aspects B-1 to B-11. Also,     preferably, such an amino acid sequence is able to specifically bind     to hCXCR4. -   Aspect C-2: Amino acid sequence, e.g. single variable domain that is     directed against hCXCR4 and that is cross-blocked from binding to     hCXCR4 by at least one of the amino acid sequences of SEQ ID NO's:     238 to 253, preferably 238 to 239. Such an amino acid sequence may     in particular be an amino acid sequence according to any of the     aspects A-1 to A-42 and/or according to aspects B-1 to B-11. Also,     preferably, such an amino acid sequence is able to specifically bind     to hCXCR4. -   Aspect C-3: Amino acid sequence, e.g. single variable domain     according to any of aspects C-1 or C-2, wherein the ability of said     amino acid sequence to cross-block or to be cross-blocked is     detected in a Biacore assay. -   Aspect C-4: Amino acid sequence, e.g. single variable domain     according to any of aspects C-1 to C-3 wherein the ability of said     amino acid sequence to cross-block or to be cross-blocked is     detected in an ELISA assay. -   Aspect D-1: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11 or C-1 to C-4, that is in     essentially isolated form. -   Aspect D-2: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D1 for     administration to a subject, wherein said amino acid sequence does     not naturally occur in said subject. -   Aspect D-3: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-2 that can specifically bind to hCXCR4 with a dissociation     constant (K_(D)) of 10⁻⁵ to 10⁻¹² moles/litre or less, and     preferably 10⁻⁷ to 10⁻¹² moles/litre or less and more preferably     10⁻⁸ to 10⁻¹² moles/litre. -   Aspect D-4: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-3 that can specifically bind to hCXCR4 with a rate of association     (k_(on)-rate) of between 10² to about 10⁷ M⁻¹s⁻¹, preferably between     10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more preferably between 10⁴ M⁻¹s⁻¹ and     10⁷ M⁻¹s⁻¹, such as between 10⁵ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹. -   Aspect D-5: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-4 that can specifically bind to hCXCR4 with a rate of dissociation     (k_(off) rate) between 1 s¹ and 10⁻⁶ s⁻¹ preferably between 10⁻² s⁻¹     and 10⁻⁶ s⁻¹, more preferably between 10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as     between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹. -   Aspect D-6: An amino acid sequence, e.g. a variable domain according     to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to D-5 that     can specifically bind to hCXCR4 with an affinity less than 500 nM,     preferably less than 200 nM, more preferably less than 10 nM, such     as less than 500 pM. -   Aspect D-7: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-6, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with 80%     sequence identity to at least one sequence selected from the group     consisting of sequences having SEQ ID NO: 238 to 253, more     preferably 238 to 239; and wherein said selected amino acid sequence     from group a) and b) binds to hCXCR4 with a dissociation constant     (K_(D)) of 10⁻⁷ to 10⁻¹² moles/liter or less. -   Aspect D-8: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-7, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with SEQ ID     NO's: 238 to 253, more preferably 238 to 239, wherein up to 10 amino     acid residues are replaced by naturally occurring amino acids and     wherein said replaced amino acids are located within the framework     regions; and wherein said selected amino acid sequence from group a)     and b) binds to at hCXCR4 with a dissociation constant (K_(D)) of     10⁻⁷ to 10⁻¹² moles/liter or less. -   Aspect D-9: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-8, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with SEQ ID     NO: 238 to 253, more preferably 238 to 239, wherein up to 8 amino     acid residues are replaced by naturally occurring amino acids and     wherein said replaced amino acids are located within the framework     regions; and wherein said selected amino acid sequence from group a)     and b) binds to hCXCR4 with a dissociation constant (K_(D)) of 10⁻⁷     to 10⁻¹² moles/liter or less. -   Aspect D-10: Amino acid sequence, e.g. single variable domain     according to any of aspects

B-1 to B-11, C-1 to C-4, and/or D-1 to D-9, wherein the amino acid sequence is selected from the group consisting of a) amino acid sequences with SEQ ID NO: 238 to 253, more preferably 238 to 239; and b) amino acid sequences with SEQ ID NO: 238 to 253, more preferably 238 to 239, wherein up to 5 amino acid residues are replaced by naturally occurring amino acids and wherein said replaced amino acids are located within the framework regions; and wherein said selected amino acid sequence from group a) and b) binds to hCXCR4 with a dissociation constant (K_(D)) of 10⁻⁷ to 10⁻¹² moles/liter or less.

-   Aspect D-11: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-10, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with SEQ ID     NO: 238 to 253, more preferably 238 to 239, wherein up to 3 amino     acid residues are replaced by naturally occurring amino acids and     wherein said replaced amino acids are located within the framework     regions; and wherein said selected amino acid sequence from group a)     and b) binds to hCXCR4 with a dissociation constant (K_(D)) of 10⁻⁷     to 10⁻¹² moles/liter or less. -   Aspect D-12: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-11, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with 80%     sequence identity to at least one sequences selected from the group     consisting of sequences having SEQ ID NO: 238 to 253, more     preferably 238 to 239; and wherein said selected amino acid sequence     from group a) and b) binds to hCXCR4 with a dissociation constant     (K_(D)) of 10⁻⁸ to 10⁻¹² moles/liter or less. -   Aspect D-13: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-12, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with sequences having SEQ ID     NO: 238 to 253, more preferably 238 to 239; and b) amino acid     sequences with sequences having SEQ ID NO: 238 to 253, more     preferably 238 to 239, wherein up to 10 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions; and     wherein said selected amino acid sequence from group a) and b) binds     to hCXCR4 with a dissociation constant (K_(D)) of 10⁻⁸ to 10⁻¹²     moles/liter or less. -   Aspect D-14: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-13, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with SEQ ID     NO's: 238 to 253, more preferably 238 to 239, wherein up to 8 amino     acid residues are replaced by naturally occurring amino acids and     wherein said replaced amino acids are located within the framework     regions; and wherein said selected amino acid sequence from group a)     and b) binds to hCXCR4 with a dissociation constant (K_(D)) of 10⁻⁸     to 10⁻¹² moles/liter or less. -   Aspect D-15: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-14, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with SEQ ID     NO's: 238 to 253, more preferably 238 to 239, wherein up to 5 amino     acid residues are replaced by naturally occurring amino acids and     wherein said replaced amino acids are located within the framework     regions; and wherein said selected amino acid sequence from group a)     and b) binds to hCXCR4 with a dissociation constant (K_(D)) of 10⁻⁸     to 10⁻¹² moles/liter or less. -   Aspect D-16: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-11, C-1 to C-4, and/or D-1 to     D-15, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with SEQ ID     NO's: 238 to 253, more preferably 238 to 239, wherein up to 3 amino     acid residues are replaced by naturally occurring amino acids and     wherein said replaced amino acids are located within the framework     regions; and wherein said selected amino acid sequence from group a)     and b) binds to hCXCR4 with a dissociation constant (K_(D)) of 10⁻⁸     to 10⁻¹² moles/liter or less.     The amino acid sequences according to aspects D-1 to D-16 may in     particular be an amino acid sequence according to any of the aspects     A-1 to A-42. -   Aspect B-12: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCD4, and that     comprises one or more stretches of amino acid residues chosen from     the group consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more         preferably 287;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 284 to 287, more preferably 287;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 284 to 287, more preferably 287;     -   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more         preferably 295;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 292 to 295, more preferably 295;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 292 to 295, more preferably 295;     -   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more         preferably 303;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 300 to 303, more preferably 303;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 300 to 303, more preferably 303;     -   or any suitable combination thereof.         Such an amino acid sequence may in particular be an amino acid         sequence according to any of the aspects A-1 to A-42. -   Aspect B-13: Amino acid sequence, e.g. single variable domain     according to aspect B-12, in which at least one of said stretches of     amino acid residues forms part of the antigen binding site for     binding against hCD4. -   Aspect B-14: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCD4 and that     comprises two or more stretches of amino acid residues chosen from     the group consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more         preferably 287;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 284 to 287, more preferably 287;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 284 to 287, more preferably 287;     -   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more         preferably 295;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 292 to 295, more preferably 295;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 292 to 295, more preferably 295;     -   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more         preferably 303;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 300 to 303, more preferably 303;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 300 to 303, more preferably 303;     -   such that (i) when the first stretch of amino acid residues         corresponds to one of the amino acid sequences according to         a), b) or c), the second stretch of amino acid residues         corresponds to one of the amino acid sequences according to d),         e), f), g), h) or i); (ii) when the first stretch of amino acid         residues corresponds to one of the amino acid sequences         according to d), e) or f), the second stretch of amino acid         residues corresponds to one of the amino acid sequences         according to a), b), c), g), h) or i); or (iii) when the first         stretch of amino acid residues corresponds to one of the amino         acid sequences according to g), h) or i), the second stretch of         amino acid residues corresponds to one of the amino acid         sequences according to a), b), c), d), e) or f).         Such an amino acid sequence may in particular be an amino acid         sequence according to any of the aspects A-1 to A-42, B-12 or         B-13. -   Aspect B-15: Amino acid sequence, e.g. single variable domain     according to aspect B-14, in which the at least two stretches of     amino acid residues forms part of the antigen binding site for     binding against hCD4. -   Aspect B-16: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCD4 and that     comprises three or more stretches of amino acid residues, in which     the first stretch of amino acid residues is chosen from the group     consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more         preferably 287;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 284 to 287, more preferably 287;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 284 to 287, more preferably 2873;     -   the second stretch of amino acid residues is chosen from the         group consisting of:     -   d) the amino acid sequences of SEQ ID NO's: 292 to 295, more         preferably 295;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 292 to 295, more preferably 295;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 292 to 295, more preferably 295;     -   and the third stretch of amino acid residues is chosen from the         group consisting of:     -   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more         preferably 303;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 300 to 303, more preferably 303;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 300 to 303, more preferably 303.         Such an amino acid sequence may in particular be an amino acid         sequence according to any of the aspects A-1 to A-42 and/or B-12         to B-15. -   Aspect B-17: Amino acid sequence, e.g. single variable domain     according to aspect B-16, in which the at least three stretches of     amino acid residues forms part of the antigen binding site for     binding against hCD4. -   Aspect B-18: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCD4 in which     the CDR sequences of said amino acid sequence have at least 70%     amino acid identity, preferably at least 80% amino acid identity,     more preferably at least 90% amino acid identity, such as 95% amino     acid identity or more or even essentially 100% amino acid identity     with the CDR sequences of at least one of the amino acid sequences     of SEQ ID NO's: 308 to 311, preferably 311. Such an amino acid     sequence may in particular be an amino acid sequence according to     any of the aspects A-1 to A-42 and/or B-12 to B-17. -   Aspect B-19: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCXCR4,     wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO'S: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO'S: 308 to     311, preferably 311, wherein up to 10 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions. -   Aspect B-20: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCXCR4,     wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO'S: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO'S: 308 to     311, preferably 311, wherein up to S amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions. -   Aspect B-21: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCXCR4,     wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO'S: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO: 308 to     311, preferably 311, wherein up to 5 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions. -   Aspect B-22: Amino acid sequence, e.g. single variable domain that     is directed against and/or that can specifically bind hCXCR4,     wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO'S: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO'S: 308 to     311, preferably 311, wherein up to 3 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions. -   Aspect C-5: Amino acid sequence, e.g. single variable domain that is     directed against hCD4 and that cross-blocks the binding of at least     one of the amino acid sequences of SEQ ID NO's: 308 to 311,     preferably 311 to hCD4. Such an amino acid sequence may in     particular be an amino acid sequence according to any of the aspects     A-1 to A-42 and/or according to aspects B-12 to B-22. Also,     preferably, such an amino acid sequence is able to specifically bind     to hCD4. -   Aspect C-6: Amino acid sequence, e.g. single variable domain that is     directed against hCD4 and that is cross-blocked from binding to hCD4     by at least one of the amino acid sequences of SEQ ID NO's: 308 to     311, preferably 311. Such an amino acid, sequence may in particular     be an amino acid sequence according to any of the aspects A-1 to     A-42 and/or according to aspects B-12 to B-22. Also, preferably,     such an amino acid sequence is able to specifically bind to hCD4. -   Aspect C-7: Amino acid sequence, e.g. single variable domain     according to any of aspects C-1 or C-2, wherein the ability of said     amino acid sequence to cross-block or to be cross-blocked is     detected in a Biacore assay. -   Aspect C-8: Amino acid sequence, e.g. single variable domain     according to any of aspects C-1 to C-3 wherein the ability of said     amino acid sequence to cross-block or to be cross-blocked is     detected in an ELISA assay. -   Aspect D-17: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, that is in     essentially isolated form. -   Aspect D-18: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     for administration to a subject, wherein said amino acid sequence     does not naturally occur in said subject. -   Aspect D-19: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-18 that can specifically bind to hCD4 with a dissociation     constant (K_(D)) of 10⁻⁵ to 10⁻¹² moles/litre or less, and     preferably 10⁻⁷ to 10⁻¹² moles/litre or less and more preferably     10⁻⁸ to 10⁻¹² moles/litre. -   Aspect D-20: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-19 that can specifically bind to hCD4 with a rate of     association (k_(on)-rate) of between 10² M⁻¹s⁻¹ to about 10⁷ M⁻¹s⁻¹,     preferably between 10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more preferably     between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, such as between 10⁵ M⁻¹s⁻¹ and     10⁷ M⁻¹s⁻¹. -   Aspect D-21: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-20 that can specifically bind to hCD4 with a rate of     dissociation (k_(off) rate) between 1 s⁻¹ and 10⁻⁶ s⁻¹ preferably     between 10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more preferably between 10⁻³ s⁻¹ and     10⁻⁶ s⁻¹, such as between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹. -   Aspect D-22: An amino acid sequence, e.g. a variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-21 that can specifically bind to hCD4 with an affinity less     than 500 nM, preferably less than 200 nM, more preferably less than     10 nM, such as less than 500 pM. -   Aspect D-23: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-22, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 238 to 253,     more preferably 238 to 239; and b) amino acid sequences with 80%     sequence identity to at least one sequence selected from the group     consisting of sequences having SEQ ID NO: 238 to 253, more     preferably 238 to 239; and wherein said selected amino acid sequence     from group a) and b) binds to hCD4 with a dissociation constant     (K_(D)) of 10⁻⁷ to 10⁻¹² moles/liter or less. -   Aspect D-24: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-23, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO's: 308 to     311, preferably 311, wherein up to 10 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions; and     wherein said selected amino acid sequence from group a) and b) binds     to at hCD4 with a dissociation constant (K_(D)) of 10⁻⁷ to 10⁻¹²     moles/liter or less. -   Aspect D-25: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-24, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO: 308 to     311, preferably 311, wherein up to 8 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions; and     wherein said selected amino acid sequence from group a) and b) binds     to hCD4 with a dissociation constant (K_(D)) of 10⁻⁷ to 10⁻¹²     moles/liter or less. -   Aspect D-26: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-25, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO: 308 to     311, preferably 311, wherein up to 5 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions; and     wherein said selected amino acid sequence from group a) and b) binds     to hCD4 with a dissociation constant (K_(D)) of 10⁻⁷ to 10⁻¹²     moles/liter or less. -   Aspect D-27: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-26, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO: 308 to     311, preferably 311, wherein up to 3 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions; and     wherein said selected amino acid sequence from group a) and b) binds     to hCD4 with a dissociation constant (K_(D)) of 10⁻⁷ to 10⁻¹²     moles/liter or less. -   Aspect D-28: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-27, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID s: 308 to 311,     preferably 311; and b) amino acid sequences with 80% sequence     identity to at least one sequences selected from the group     consisting of sequences having SEQ ID NO: 308 to 311, preferably     311; and wherein said selected amino acid sequence from group a)     and b) binds to hCD4 with a dissociation constant (K_(D)) of 10⁻⁸ to     10⁻¹² moles/liter or less. -   Aspect D-29: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-28, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with sequences having SEQ ID     NO: 308 to 311, preferably 311; and b) amino acid sequences with     sequences having SEQ ID NO: 308 to 311, preferably 311, wherein up     to 10 amino acid residues are replaced by naturally occurring amino     acids and wherein said replaced amino acids are located within the     framework regions; and wherein said selected amino acid sequence     from group a) and b) binds to hCD4 with a dissociation constant     (K_(D)) of 10⁻⁸ to 10⁻¹² moles/liter or less. -   Aspect D-30: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-29, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO's: 308 to     311, preferably 311, wherein up to 8 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions; and     wherein said selected amino acid sequence from group a) and b) binds     to hCD4 with a dissociation constant (K_(D)) of 10⁻⁸ to 10⁻¹²     moles/liter or less. -   Aspect D-31: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-30, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO's: 308 to     311, preferably 311, wherein up to 5 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions; and     wherein said selected amino acid sequence from group a) and b) binds     to hCD4 with a dissociation constant (K_(D)) of 10⁻⁸ to 10⁻¹²     moles/liter or less. -   Aspect D-32: Amino acid sequence, e.g. single variable domain     according to any of aspects B-12 to B-22 or C-5 to C-8, and/or D-17     to D-31, wherein the amino acid sequence is selected from the group     consisting of a) amino acid sequences with SEQ ID NO's: 308 to 311,     preferably 311; and b) amino acid sequences with SEQ ID NO's: 308 to     311, preferably 311, wherein up to 3 amino acid residues are     replaced by naturally occurring amino acids and wherein said     replaced amino acids are located within the framework regions; and     wherein said selected amino acid sequence from group a) and b) binds     to hCD4 with a dissociation constant (K_(D)) of 10⁻⁸ to 10⁻¹²     moles/liter or less.     The amino acid sequences according to aspects D-17 to D-32 may in     particular be an amino acid sequence according to any of the aspects     A-1 to A-42. -   Aspect E-1: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, that is a naturally occurring amino acid sequence (from any     suitable species) or a synthetic or semi-synthetic amino acid     sequence. -   Aspect E-2: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 that comprises an immunoglobulin fold or that under     suitable conditions is capable of forming an immunoglobulin fold. -   Aspect E-3: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 or E-2, that is an immunoglobulin sequence. -   Aspect E-4: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-3, that is a naturally occurring     immunoglobulin sequence (from any suitable species) or a synthetic     or semi-synthetic immunoglobulin sequence. -   Aspect E-5: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-4 that is a humanized immunoglobulin sequence,     a camelized immunoglobulin sequence or an immunoglobulin sequence     that has been obtained by techniques such as affinity maturation. -   Aspect E-6: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-5 that essentially consists of a light chain     variable domain sequence (e.g. a V_(L)-sequence); or of a heavy     chain variable domain sequence (e.g. a V_(H)-sequence). -   Aspect E-7: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-6, that essentially consists of a heavy chain     variable domain sequence that is derived from a conventional     four-chain antibody or that essentially consist of a heavy chain     variable domain sequence that is derived from heavy chain antibody. -   Aspect E-8: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, that essentially consists of a domain antibody (or an amino     acid sequence that is suitable for use as a domain antibody), of a     single domain antibody (or an amino acid sequence that is suitable     for use as a single domain antibody), of a “dAb” (or an amino acid     sequence that is suitable for use as a dAb) or of a Nanobody     (including but not limited to a V_(HH) sequence). -   Aspect E-9: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-8 that essentially consists of a Nanobody. -   Aspect E-10: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-9 that essentially consists of a Nanobody that     -   i) has at least 80% amino acid identity with at least one of the         amino acid sequences of SEQ ID NO's: 1 to 22, in which for the         purposes of determining the degree of amino acid identity, the         amino acid residues that form the CDR sequences are disregarded;     -   and in which:     -   ii) preferably one or more of the amino acid residues at         positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according         to the Kabat numbering are chosen from the Hallmark residues         mentioned in Table A-3. -   Aspect E-11: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-10, that essentially consists of a Nanobody     that     -   i) has at least 80% amino acid identity with at least one of the         amino acid sequences of SEQ ID NO's: 238 to 253, more preferably         238 to 239 and SEQ ID NO's: 308 to 311, more preferably 311, in         which for the purposes of determining the degree of amino acid         identity, the amino acid residues that form the CDR sequences         are disregarded;     -   and in which:     -   ii) preferably one or more of the amino acid residues at         positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according         to the Kabat numbering are chosen from the Hallmark residues         mentioned in Table A-3. -   Aspect E-12: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-11, that essentially consists of a humanized     Nanobody. -   Aspect E-13: Amino acid sequence, e.g. single variable domain     according to any of aspects B-1 to B-22 or C-1 to C-8, and/or D-1 to     D-32, and/or E-1 to E-11, that in addition to the at least one     binding site for binding formed by the CDR sequences, contains one     or more further binding sites for binding against other antigens,     proteins or targets.     The amino acid sequences according to aspects E-1 to E-13 may in     particular be an amino acid sequence according to any of the aspects     A-1 to A-42. -   Aspect F-1: Amino acid sequence, e.g. single variable domain that     essentially consists of 4 framework regions (FR1 to FR4,     respectively) and 3 complementarity determining regions (CDR1 to     CDR3, respectively), in which:     -   CDR1 is chosen from the group consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more         preferably 142 to 143;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 142 to 157, more preferably 142 to 143;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 142 to 157, more preferably 142 to 143;     -   and/or     -   CDR2 is chosen from the group consisting of:     -   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more         preferably 174 to 175;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 174 to 189, more preferably 174 to 175;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 174 to 189, more preferably 174 to 175;     -   and/or     -   CDR3 is chosen from the group consisting of:     -   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more         preferably 206 to 207;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 206 to 221, more preferably 206 to 207;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 206 to 221, more preferably 206 to 207.         Such an amino acid sequence is preferably directed against         hCXCR4 and/or an amino acid sequence that can specifically bind         to hCXCR4. Also, such an amino acid sequence is preferably an         amino acid sequence according to any of the aspects A-1 to A-42,         C-1 to C-4, D1 to D-16 and/or E-1 to E-13. -   Aspect F-2: Amino acid sequence, e.g. single variable domain that     essentially consists of 4 framework regions (FR1 to FR4,     respectively) and 3 complementarity determining regions (CDR1 to     CDR3, respectively), in which:     -   CDR1 is chosen from the group consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 142 to 157, more         preferably 142 to 143;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 142 to 157, more preferably 142 to 143;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 142 to 157, more preferably 142 to 143;     -   and     -   CDR2 is chosen from the group consisting of:     -   d) the amino acid sequences of SEQ ID NO's: 174 to 189, more         preferably 174 to 175;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 174 to 189, more preferably 174 to 175;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 174 to 189, more preferably 174 to 175;     -   and     -   CDR3 is chosen from the group consisting of:     -   g) the amino acid sequences of SEQ ID NO's: 206 to 221, more         preferably 206 to 207;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 206 to 221, more preferably 206 to 207;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 206 to 221, more preferably 206 to 207.         Such an amino acid sequence is preferably directed against         hCXCR4 and/or an amino acid sequence that can specifically bind         to hCXCR4. Also, such an amino acid sequence is preferably an         amino acid sequence according to any of the aspects A-1 to A-42,         C-1 to C-4, D1 to D-16 and/or E-1 to E-13, -   Aspect F-3: An amino acid sequence according to any of aspects F-1     and F-2, in which the CDR sequences of said amino acid sequence have     at least 70% amino acid identity, preferably at least 80% amino acid     identity, more preferably at least 90% amino acid identity, such as     95% amino acid identity or more or even essentially 100% amino acid     identity with the CDR sequences of at least one of the amino acid     sequences of SEQ ID NO's: 238 to 253, more preferably 238 to 239.     Such an amino acid sequence is preferably directed against hCXCR4     and/or an amino acid sequence that can specifically bind to hCXCR4.     Also, such an amino acid sequence is preferably an amino acid     sequence according to any of the aspects A-1 to A-42, C-1 to C-4, D1     to D-16 and/or E-1 to E-13. -   Aspect F-4: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-3 that is directed against     hCXCR4 and that cross-blocks the binding to hCXCR4 of at least one     of the amino acid sequences according to any of aspects the amino     acid sequences of SEQ ID NO's: 238 to 253, more preferably 238 to     239. -   Aspect F-5: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-3 that is directed against     hCXCR4 and that is cross-blocked from binding to hCXCR4 by at least     one of the amino acid sequences of SEQ ID NO's: 238 to 253, more     preferably 238 to 239. -   Aspect F-6: Amino acid sequence, e.g. single variable domain     according to any of aspects F-4 or F-5 wherein the ability of said     amino acid sequence to cross-block or to be cross-blocked is     detected in a Biacore assay. -   Aspect F-7: Amino acid sequence, e.g. single variable domain     according to any of aspects F4 or F-5 wherein the ability of said     amino acid sequence to cross-block or to be cross-blocked is     detected in an ELISA assay. -   Aspect F-8: Amino acid sequence, e.g. single variable domain that     essentially consists of 4 framework regions (FR1 to FR4,     respectively) and 3 complementarity determining regions (CDR1 to     CDR3, respectively), in which:     -   CDR1 is chosen from the group consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more         preferably 287;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 284 to 287, more preferably 287;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 284 to 287, more preferably 287;     -   and/or     -   CDR2 is chosen from the group consisting of:     -   the amino acid sequences of SEQ ID NO's: 293 to 295, more         preferably 295;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 293 to 295, more preferably 295;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 293 to 295, more preferably 295;     -   and/or     -   CDR3 is chosen from the group consisting of:     -   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more         preferably 303;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 300 to 303, more preferably 303;     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 300 to 303, more preferably 303.         Such an amino acid sequence is preferably directed against hCD4         and/or an amino acid sequence that can specifically bind to         hCD4. Also, such an amino acid sequence is preferably an amino         acid sequence according to any of the aspects A-1 to A-42, C-5         to C-8, D-17 to D-32 and/or E-1 to E-13. -   Aspect F-9: Amino acid sequence, e.g. single variable domain that     essentially consists of 4 framework regions (FR1 to FR4,     respectively) and 3 complementarity determining regions (CDR1 to     CDR3, respectively), in which:     -   CDR1 is chosen from the group consisting of:     -   a) the amino acid sequences of SEQ ID NO's: 284 to 287, more         preferably 287;     -   b) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 284 to 287, more preferably 287;     -   c) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 284 to 287, more preferably 287;     -   and     -   CDR2 is chosen from the group consisting of:     -   d) the amino acid sequences of SEQ ID NO's: 293 to 295, more         preferably 295;     -   e) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 293 to 295, more preferably 295;     -   f) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 293 to 295, more preferably 295;     -   and     -   CDR3 is chosen from the group consisting of:     -   g) the amino acid sequences of SEQ ID NO's: 300 to 303, more         preferably 303;     -   h) amino acid sequences that have at least 80% amino acid         identity with at least one of the amino acid sequences of SEQ ID         NO's: 300 to 303, more preferably 303:     -   i) amino acid sequences that have 3, 2, or 1 amino acid         difference with at least one of the amino acid sequences of SEQ         ID NO's: 300 to 303, more preferably 303.         Such an amino acid sequence is preferably directed against hCD4         and/or an amino acid sequence that can specifically bind to         hCD4. Also, such an amino acid sequence is preferably an amino         acid sequence according to any of the aspects A-1 to A-42, C-5         to C-8, D-17 to D-32 and/or E-1 to E-13. -   Aspect F-10: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 and F-2, in which the CDR sequences     of said amino acid sequence have at least 70% amino acid identity,     preferably at least 80% amino acid identity, more preferably at     least 90% amino acid identity, such as 95% amino acid identity or     more or even essentially 100% amino acid identity with the CDR     sequences of at least one of the amino acid sequences of SEQ ID     NO's: 308 to 311, more preferably 311.     Such an amino acid sequence is preferably directed against hCD4     and/or an amino acid sequence that can specifically bind to hCD4.     Also, such an amino acid sequence is preferably an amino acid     sequence according to any of the aspects A-1 to A-42, C-5 to C-8,     D-17 to D-32 and/or E-1 to E-13. -   Aspect F-11: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-3 that is directed against hCD4     and that cross-blocks the binding to hCD4 of at least one of the     amino acid sequences according to any of aspects the amino acid     sequences of SEQ ID NO's: 308 to 311, more preferably 311. -   Aspect F-12: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-3 that is directed against     hCXCR4 and that is cross-blocked from binding to hCD4 by at least     one of the amino acid sequences of SEQ ID NO's: 308 to 311, more     preferably 311. -   Aspect F-13: Amino acid sequence, e.g. single variable domain     according to any of aspects F-4 or F-5 wherein the ability of said     amino acid sequence to cross-block or to be cross-blocked is     detected in a Biacore assay. -   Aspect F-14: Amino acid sequence, e.g. single variable domain     according to any of aspects F4 or F-5 wherein the ability of said     amino acid sequence to cross-block or to be cross-blocked is     detected in an ELISA assay. -   Aspect F-15: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-14, that is in essentially     isolated form. -   Aspect F-16: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-15, for administration to a     subject, wherein said an amino acid sequence does not naturally     occur in said subject. -   Aspect F-17: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-16, that can specifically bind     to Target of the invention with a dissociation constant (K_(D)) of     10⁻⁵ to 10⁻¹² moles/litre or less, and preferably 10⁻⁷ to 10⁻¹²     moles/litre or less and more preferably 10⁻⁸ to 10⁻¹² moles/litre. -   Aspect F-18: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-17, that can specifically bind     to Target of the invention with a rate of association (k_(on)-rate)     of between 10² M⁻¹s⁻¹ to about 10⁷ M⁻¹s⁻¹, preferably between 10³     M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more preferably between 10⁴ M⁻¹s⁻¹ and 10⁷     M⁻¹s⁻¹, such as between 10⁵ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹. -   Aspect F-19: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-18, that can specifically bind     to Target of the invention with a rate of dissociation (k_(off)     rate) between 1 s⁻¹ and 10⁻⁶ s⁻¹ preferably between 10⁻² s⁻¹ and     10⁻⁶ s⁻¹, more preferably between 10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as     between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹. -   Aspect F-20: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-19, that can specifically bind     to Target of the invention with an affinity less than 500 nM,     preferably less than 200 nM, more preferably less than 10 nM, such     as less than 500 pM. -   Aspect F-21: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-20, that is a naturally     occurring amino acid sequence (from any suitable species) or a     synthetic or semi-synthetic amino acid sequence. -   Aspect F-22: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-21, that comprises an     immunoglobulin fold or that under suitable conditions is capable of     forming an immunoglobulin fold. -   Aspect F-23: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-22, that is an immunoglobulin     sequence. -   Aspect F-24: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-23, that is a naturally     occurring immunoglobulin sequence (from any suitable species) or a     synthetic or semi-synthetic immunoglobulin sequence. -   Aspect F-25: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-24, that is a humanized     immunoglobulin sequence, a camelized immunoglobulin sequence or an     immunoglobulin sequence that has been obtained by techniques such as     affinity maturation. -   Aspect F-26: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-25, that essentially consists     of a light chain variable domain sequence (e.g. a V_(L)-sequence);     or of a heavy chain variable domain sequence (e.g. a     V_(H)-sequence). -   Aspect F-27: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-26, that essentially consists     of a heavy chain variable domain sequence that is derived from a     conventional four-chain antibody or that essentially consist of a     heavy chain variable domain sequence that is derived from heavy     chain antibody. -   Aspect F-28: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-27, that essentially consists     of a domain antibody (or an amino acid sequence that is suitable for     use as a domain antibody), of a single domain antibody (or an amino     acid sequence that is suitable for use as a single domain antibody),     of a “dAb” (or an amino acid sequence that is suitable for use as a     dAb) or of a Nanobody (including but not limited to a V_(HH)     sequence). -   Aspect F-29: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-28, that essentially consists     of a Nanobody. -   Aspect F-30: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-29, that essentially consists     of a Nanobody that     -   i) has at least 80% amino acid identity with at least one of the         amino acid sequences of SEQ ID NO's: 1 to 22, in which for the         purposes of determining the degree of amino acid identity, the         amino acid residues that form the CDR sequences are disregarded;     -   and in which:     -   ii) preferably one or more of the amino acid residues at         positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according         to the Kabat numbering are chosen from the Hallmark residues         mentioned in Table B-2. -   Aspect F-31: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-30, that essentially consists     of a Nanobody that     -   i) has at least 80% amino acid identity with at least one of the         amino acid sequences of SEQ ID NO's: 238 to 253, preferably 238         to 239 and SEQ ID NO's: 308 to 311, preferably 311, in which for         the purposes of determining the degree of amino acid identity,         the amino acid residues that form the CDR sequences are         disregarded;     -   and in which:     -   ii) preferably one or more of the amino acid residues at         positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according         to the Kabat numbering are chosen from the Hallmark residues         mentioned in Table A-3. -   Aspect F-32: Amino acid sequence, e.g. single variable domain     according to any of aspects F-1 to F-31, that essentially consists     of a humanized Nanobody. -   Aspect G-1: Amino acid sequence, e.g. single variable domain     according to any of the preceding aspects, that in addition to the     at least one binding site for binding formed by the CDR sequences,     contains one or more further binding sites for binding against     another antigen, protein or target. -   Aspect K-1: Polypeptide that comprises or essentially consists of     one or more amino acid sequences according to any of aspects A-1 to     A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32     or G-1, and optionally further comprises one or more other amino     acid binding units, optionally linked via one or more peptidic     linkers. -   Aspect K-2: Polypeptide according to aspect K-1, in which said one     or more other amino acid binding units are immunoglobulin sequences. -   Aspect K-3: Polypeptide according to any of aspects K-1 or K-2, in     which said one or more other amino acid binding units are chosen     from the group consisting of domain antibodies, amino acid sequences     that are suitable for use as a domain antibody, single domain     antibodies, amino acid sequences that are suitable for use as a     single domain antibody, “dAb”'s, amino acid sequences that are     suitable for use as a dAb, or Nanobodies. -   Aspect K-4: Polypeptide according to any of aspects K-1 to K-3, in     which said one or more amino acid sequences of the invention are     immunoglobulin sequences. -   Aspect K-5: Polypeptide according to any of aspects K-1 to K-4, in     which said one or more amino acid sequences of the invention are     chosen from the group consisting of domain antibodies, amino acid     sequences that are suitable for use as a domain antibody, single     domain antibodies, amino acid sequences that are suitable for use as     a single domain antibody, “dAb”'s, amino acid sequences that are     suitable for use as a dAb, or Nanobodies. -   Aspect K-6: Polypeptide according to any of aspects K-1 to K-5,     which is a multivalent construct. -   Aspect K-7: Polypeptide according to any of aspects K-1 to K-6,     which is a multiparatopic construct. -   Aspect K-8: Polypeptide according to any of aspects K-1 to K-7,     which is a multispecific construct. -   Aspect K-9: Polypeptide according to any of aspects K-1 to K-9,     which has an increased half-life, compared to the corresponding     amino acid sequence according to any of aspects A-1 to A-42, B-1 to     B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1 per     se. -   Aspect K-10: Polypeptide according to aspect K-9, in which said one     or more other binding units provide the polypeptide with increased     half-life, compared to the corresponding amino acid sequence     according to any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8,     D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1 per se. -   Aspect K-11: Polypeptide according to aspect K-9 or K-10, in which     said one or more other binding units that provide the polypeptide     with increased half-life is chosen from the group consisting of     serum proteins or fragments thereof, binding units that can bind to     serum proteins, an Fc portion, and small proteins or peptides that     can bind to serum proteins. -   Aspect K-12: Polypeptide according to any of aspects K-9 to K-11, in     which said one or more other binding units that provide the     polypeptide with increased half-life is chosen from the group     consisting of human serum albumin or fragments thereof. -   Aspect K-13: Polypeptide according to any of aspect K-9 to K-12, in     which said one or more other binding units that provides the     polypeptide with increased half-life are chosen from the group     consisting of binding units that can bind to serum albumin (such as     human serum albumin) or a serum immunoglobulin (such as IgG). -   Aspect K-14: Polypeptide according to any of aspects K-9 to K-13, in     which said one or more other binding units that provides the     polypeptide with increased half-life are chosen from the group     consisting of domain antibodies, amino acid sequences that are     suitable for use as a domain antibody, single domain antibodies,     amino acid sequences that are suitable for use as a single domain     antibody, “dAb”'s, amino acid sequences that are suitable for use as     a dAb, or Nanobodies that can bind to serum albumin (such as human     serum albumin) or a serum immunoglobulin (such as IgG). -   Aspect K-15: Polypeptide according to aspect K-9 to K-14, in which     said one or more other binding units that provides the polypeptide     with increased half-life is a Nanobody that can bind to serum     albumin (such as human serum albumin) or a serum immunoglobulin     (such as IgG). -   Aspect K-16: Polypeptide according to any of aspects K-9 to K-15,     that has a serum half-life that is at least 1.5 times, preferably at     least 2 times, such as at least 5 times, for example at least 10     times or more than 20 times, greater than the half-life of the     corresponding amino acid sequence according to any of aspects A-1 to     A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32     or G-1 per se. -   Aspect K-17: Polypeptide according to any of aspects K-9 to K-16,     that has a serum half-life that is increased with more than 1 hours,     preferably more than 2 hours, more preferably more than 6 hours,     such as more than 12 hours, or even more than 24, 48 or 72 hours,     compared to the corresponding amino acid sequence according to any     of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to     E-13, F-1 to F-32 or G-1 per se. -   Aspect K-18: Polypeptide according to any of aspects K-1 to K-17,     that has a serum half-life in human of at least about 12 hours,     preferably at least 24 hours, more preferably at least 48 hours,     even more preferably at least 72 hours or more; for example, of at     least 5 days (such as about 5 to 10 days), preferably at least 9     days (such as about 9 to 14 days), more preferably at least about 10     days (such as about 10 to 15 days), or at least about 11 days (such     as about 11 to 16 days), more preferably at least about 12 days     (such as about 12 to 18 days or more), or more than 14 days (such as     about 14 to 19 days). -   Aspect L-1: Compound or construct, that comprises or essentially     consists of one or more amino acid sequences according to any of     aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to     E-13, F-1 to F-32 or G-1, and optionally further comprises one or     more other groups, residues, moieties or binding units, optionally     linked via one or more linkers. -   Aspect L-2: Compound or construct according to aspects L-1, in which     said one or more other groups, residues, moieties or binding units     are amino acid sequences. -   Aspect L-3: Compound or construct according to aspect L-1 or L-2, in     which said one or more linkers, if present, are one or more amino     acid sequences. -   Aspect L-4: Compound or construct according to any of aspects L-1 to     L-3, in which said one or more other groups, residues, moieties or     binding units are immunoglobulin sequences. -   Aspect L-5: Compound or construct according to any of aspects L-1 to     L-4, in which said one or more other groups, residues, moieties or     binding units are chosen from the group consisting of domain     antibodies, amino acid sequences that are suitable for use as a     domain antibody, single domain antibodies, amino acid sequences that     are suitable for use as a single domain antibody, “dAb”'s, amino     acid sequences that are suitable for use as a dAb, or Nanobodies. -   Aspect L-6: Compound or construct according to any of aspects L-1 to     L-5, in which said one or more amino acid sequences of the invention     are immunoglobulin sequences. -   Aspect L-7: Compound or construct according to any of aspects L-1 to     L-6, in which said one or more amino acid sequences of the invention     are chosen from the group consisting of domain antibodies, amino     acid sequences that are suitable for use as a domain antibody,     single domain antibodies, amino acid sequences that are suitable for     use as a single domain antibody, “dAb”'s, amino acid sequences that     are suitable for use as a dAb, or Nanobodies. -   Aspect L-8: Compound or construct according to any of aspects L-1 to     L-8, which is a multivalent construct. -   Aspect L-9: Compound or construct according to aspect L-8, which is     a bivalent construct. -   Aspect L-10: Compound or construct according to aspect L-9, which     comprises two amino acid sequences that are directed against and/or     capable of binding to the CXCL12 binding site on hCXCR4. -   Aspect L-11: Compound or construct according to any of aspects L-9     to L10, which comprises two amino acid sequences that are capable of     competing with CXCL12 for binding to hCXCR4. -   Aspect L-12: Compound or construct according to any of aspects L-10     to L-14 which can simultaneously bind both binding sites on hCXCR4. -   Aspect L-13: Compound or construct according to any of aspects L-9     to L-12 which neutralizes HIV. -   Aspect L-14: Compound or construct according to aspect L-9, which     comprises two amino acid sequences that are directed against and/or     capable of binding to the gp120 binding site on hCD4. -   Aspect L-5: Compound or construct according to any of aspects L-9 or     L-14, which comprises two amino acid sequences that are capable of     competing with gp120 for binding to hCD4. -   Aspect L-16: Compound or construct according to any of aspects L-14     to L-15 which can simultaneously bind both binding sites on hCD4. -   Aspect L-17: Compound or construct according to any of aspects L-14     to L-16 which neutralizes HIV. -   Aspect L-18: Compound or construct according to any of aspects L-1     to L-8, which is a multiparatopic construct. -   Aspect L-19: Compound or construct according to aspect L-18, which     is a biparatopic construct. -   Aspect L-20: Compound or construct according to aspects L-19, which     comprises at least one amino acid sequence directed against a first     antigenic determinant, epitope, part or domain of a Target of the     invention and at least one amino acid sequence directed against a     second antigenic determinant, epitope, part or domain of the Target     of the invention different from the first antigenic determinant,     epitope, part or domain. -   Aspect L-21: Biparatopic compound or construct according to aspect     L-20, which is capable of simultaneously binding to said first     antigenic determinant, epitope, part or domain of a Target of the     invention and to said second antigenic determinant, epitope, part or     domain of the Target of the invention. -   Aspect L-22: Compound or construct according to any of aspects L-18     to L-21, which comprises at least one amino acid sequence directed     against a first antigenic determinant, epitope, part or domain of     hCXCR4 and at least one amino acid sequence directed against a     second antigenic determinant, epitope, part or domain of hCXCR4     different from the first antigenic determinant, epitope, part or     domain. -   Aspect L-23: Biparatopic compound or construct according to aspect     L-22, which is capable of simultaneously binding to said first     antigenic determinant, epitope, part or domain of hCXCR4 and to said     second antigenic determinant, epitope, part or domain of hCXCR4. -   Aspect L-24: Compound or construct according to any of aspects L-22     to L-23 wherein said compound or construct competes with CXCL12 for     binding to hCXCR4. -   Aspect L-25: Compound or construct according to aspects L-24,     wherein said compound or construct inhibits and/or blocks binding of     CXCL12 to hCXCR4. -   Aspect L-26: Compound or construct according to any of aspects L-24     to L-25, wherein said compound or construct is directed against the     CXCL12 binding site on hCXCR4. -   Aspect L-27: Compound or construct according to any of aspects L-24     to L-26, which comprises at least one amino acid sequence that is     directed against and/or capable of binding to the CXCL12 binding     site on hCXCR4 and at least one further amino acid sequence that is     capable of binding to at least one other antigenic determinant,     epitope, part or domain on hCXCR4. -   Aspect L-28: Compound or construct according to any of aspects L-24     to L-27, which comprises at least one amino acid sequence that is     capable of competing with CXCL12 for binding hCXCR4 and at least one     further amino acid sequence that is capable of binding to at least     one other antigenic determinant, epitope, part or domain of hCXCR4. -   Aspect L-29: Compound or construct according to any of aspects L-24     to L-28, which can simultaneously bind both binding sites on hCXCR4. -   Aspect L-30: Compound or construct according to aspect L-18, wherein     both paratopes are directed against the CXCL12 binding site on     hCXCR4. -   Aspect L-31: Biparatopic compound or construct according to aspect     L-30, which can simultaneously bind both binding site on hCXCR4. -   Aspect L-32: Compound or construct according to any of aspects L-18     to L-21, which comprises at least one amino acid sequence directed     against a first antigenic determinant, epitope, part or domain of     hCD4 and at least one amino acid sequence directed against a second     antigenic determinant, epitope, part or domain of hCD4 different     from the first antigenic determinant, epitope, part or domain. -   Aspect L-33: Biparatopic compound or construct according to aspect     L-32, which is capable of simultaneously binding to said first     antigenic determinant, epitope, part or domain of hCD4 and to said     second antigenic determinant, epitope, part or domain of hCD4. -   Aspect L-34: Compound or construct according to any of aspects L-32     to L-33 wherein said compound or construct competes with gp120 for     binding to hCD4. -   Aspect L-35: Compound or construct according to aspects L-34,     wherein said compound or construct inhibits and/or blocks binding of     gp120 to hCD4. -   Aspect L-36: Compound or construct according to any of aspects L-34     to L-35, wherein said compound or construct is directed against the     gp120 binding site on hCD4. -   Aspect L-37: Compound or construct according to any of aspects L-34     to L-36, which comprises at least one amino acid sequence that is     directed against and/or capable of binding to the gp120 binding site     on hCD4 and at least one further amino acid sequence that is capable     of binding to at least one other antigenic determinant, epitope,     part or domain on hCD4. -   Aspect L-38: Compound or construct according to any of aspects L-34     to L-37, which comprises at least one amino acid sequence that is     capable of competing with gp120 for binding hCD4 and at least one     further amino acid sequence that is capable of binding to at least     one other antigenic determinant, epitope, part or domain of hCD4. -   Aspect L-39: Compound or construct according to any of aspects L-34     to L-38, which can simultaneously bind both binding sites on hCD4. -   Aspect L-40: Compound or construct according to aspect L-18, wherein     both paratopes are directed against the gp120 binding site on hCD4. -   Aspect L-41: Biparatopic compound or construct according to aspect     L-40, which can simultaneously bind both binding site on hCD4. -   Aspect L-42: Compound or construct according to any of aspects L-1     to L-41, which is a multispecific construct. -   Aspect L-43: Compound or construct according to any of aspects L-1     to L-42, which has an increased half-life, compared to the     corresponding amino acid sequence according to any of aspects A-1 to     A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32     or G-1 per se. -   Aspect L-44: Compound or construct according to aspect L-1 to L-43,     in which said one or more other groups, residues, moieties or     binding units provide the compound or construct with increased     half-life, compared to the corresponding amino acid sequence     according to any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8,     D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1 per se. -   Aspect L-45: Compound or construct according to aspect L-44, in     which said one or more other groups, residues, moieties or binding     units that provide the compound or construct with increased     half-life is chosen from the group consisting of serum proteins or     fragments thereof, binding units that can bind to serum proteins, an     Fc portion, and small proteins or peptides that can bind to serum     proteins. -   Aspect L-46: Compound or construct according to aspect L-44 or L-45,     in which said one or more other groups, residues, moieties or     binding units that provide the compound or construct with increased     half-life is chosen from the group consisting of human serum albumin     or fragments thereof. -   Aspect L-47: Compound or construct according to any of aspects L-44     to L-46, in which said one or more other groups, residues, moieties     or binding units that provides the compound or construct with     increased half-life are chosen from the group consisting of binding     units that can bind to serum albumin (such as human serum albumin)     or a serum immunoglobulin (such as IgG). -   Aspect L-48: Compound or construct according to any of aspects L-44     to L-46, in which said one or more other groups, residues, moieties     or binding units that provides the compound or construct with     increased half-life are chosen from the group consisting of domain     antibodies, amino acid sequences that are suitable for use as a     domain antibody, single domain antibodies, amino acid sequences that     are suitable for use as a single domain antibody, “dAb”'s, amino     acid sequences that are suitable for use as a dAb, or Nanobodies     that can bind to serum albumin (such as human serum albumin) or a     serum immunoglobulin (such as IgG). -   Aspect L-49: Compound or construct according to any of aspects L-44     to L-46, in which said one or more other groups, residues, moieties     or binding units that provides the compound or construct with     increased half-life is a Nanobody that can bind to serum albumin     (such as human serum albumin) or a serum immunoglobulin (such as     IgG). -   Aspect L-50: Compound or construct according to any of aspects L-43     to L-49, that has a serum half-life that is at least 1.5 times,     preferably at least 2 times, such as at least 5 times, for example     at least 10 times or more than 20 times, greater than the half-life     of the corresponding amino acid sequence according to any of aspects     A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1     to F-32 or G-1 per se. -   Aspect L-51: Compound or construct according to any of aspects L-43     to L-50, that has a serum half-life that is increased with more than     1 hours, preferably more than 2 hours, more preferably more than 6     hours, such as more than 12 hours, or even more than 24, 48 or 72     hours, compared to the corresponding amino acid sequence according     to any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32,     E-1 to E-13, F-1 to F-32 or G-1 per se. -   Aspect L-52: Compound or construct according to any of aspects L-43     to L-51, that has a serum half-life in human of at least about 12     hours, preferably at least 24 hours, more preferably at least 48     hours, even more preferably at least 72 hours or more; for example,     of at least 5 days (such as about 5 to 10 days), preferably at least     9 days (such as about 9 to 14 days), more preferably at least about     10 days (such as about 10 to 15 days), or at least about 11 days     (such as about 11 to 16 days), more preferably at least about 12     days (such as about 12 to 18 days or more), or more than 14 days     (such as about 14 to 19 days). -   Aspect H-1: Monovalent construct, comprising or essentially     consisting of one amino acid sequence according to any of aspects     A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1     to F-32 or G-1. -   Aspect H-2: Monovalent construct according to aspect H-1, in which     said amino acid sequence of the invention is chosen from the group     consisting of domain antibodies, amino acid sequences that are     suitable for use as a domain antibody, single domain antibodies,     amino acid sequences that are suitable for use as a single domain     antibody, “dAb”'s, amino acid sequences that are suitable for use as     a dAb, or Nanobodies. -   Aspect H-3: Monovalent construct, that is chosen from the group     consisting of SEQ ID NO's: 238 to 253, preferably 238 to 239 and SEQ     ID NO's: 308 to 311, preferably 311 or from the group consisting of     amino acid sequences that have more than 80%, preferably more than     90%, more preferably more than 95%, such as 99% or more sequence     identity (as defined herein) with at least one of the amino acid     sequences of SEQ ID NO's: 238 to 253, preferably 238 to 239 and SEQ     ID NO's: 308 to 311, preferably 311. -   Aspect H-4: Use of a monovalent construct according to any of     aspects H-1 to H-3, in preparing a multivalent compound or construct     according to any of aspects L-8 to L-42. -   Aspect H-5: Use of a monovalent construct according to aspect H-4,     in preparing a multiparatopic construct such as a bivalent,     biparatopic, trivalent, triparatopic construct. -   Aspect H-6: Use of a monovalent construct according to any of     aspects H-4 or H-5, wherein the monovalent construct is used as a     binding domain or binding unit in preparing a multivalent construct     comprising two or more binding units. -   Aspect H-7: Use of a monovalent construct according to any of     aspects H-4 to H-6, in preparing a multivalent construct that     exhibits intramolecular binding compared to intermolecular binding. -   Aspect H-8: Use of a monovalent construct according to any of     aspects H-4 to H-7, as a binding domain or binding unit in preparing     a multivalent construct, wherein the binding domains or binding     units are linked via a linker such that the multivalent construct     preferably exhibits intramolecular binding compared to     intermolecular binding. -   Aspect H-9: Use of a monovalent construct according to any of     aspects H-4 to H-8, wherein the monovalent construct is directed     against the CXCL12 binding site on hCXCR4 and/or is capable of     competing with CXCL12 for binding hCXCR4. -   Aspect H-10: Use of two monovalent constructs according to any of     aspects H-4 to H-9 for the preparation of a bivalent compound or     construct, wherein the monovalent constructs are directed against     the CXCL12 binding site on hCXCR4 and/or capable of competing with     CXCL12 for binding hCXCR4. -   Aspect H-11: Use of a monovalent construct according to any of     aspects H-4 to H-8, wherein the monovalent construct is directed     against the gp120 binding site on hCD4 and/or is capable of     competing with gp120 for binding hCD4. -   Aspect H-12: Use of two monovalent constructs according to any of     aspects H-4 to H-9 for the preparation of a bivalent compound or     construct, wherein the monovalent constructs are directed against     the gp120 binding site on hCD4 and/or capable of competing with     gp120 for binding hCD4. -   Aspect M-1: Nucleic acid or nucleotide sequence, that encodes an     amino acid sequence according to any of aspects A-1 to A-42, B-1 to     B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1, a     compound or construct according to any of aspects that is such that     it can be obtained by expression of a nucleic acid or nucleotide     sequence encoding the same, or a monovalent construct according to     any of aspects H-1 to H-3. -   Aspect M-2: Nucleic acid or nucleotide sequence according to aspect     M-1, that is in the form of a genetic construct. -   Aspect M-3: Use of a nucleic acid or nucleotide sequence according     to aspect M-2, that encodes a monovalent construct according to any     of aspects H-1 to H-3, for the preparation of a genetic construct     that encodes a multivalent construct according to any of aspects L-8     to L-42. -   Aspect M-4: Use of a nucleic acid or nucleotide sequence according     to aspect M-3, wherein the genetic construct encodes a     multiparatopic (such as a biparatopic) construct. -   Aspect N-1: Host or host cell that expresses, or that under suitable     circumstances is capable of expressing, an amino acid sequence     according to any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8,     D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1, a polypeptide     according to any of aspects K-1 to K-18, a compound or construct     according to any of aspects L-1 to L-52 that is such that it can be     obtained by expression of a nucleic acid or nucleotide sequence     encoding the same, or a monovalent construct according to any of     aspects H-1 or H-3; and/or that comprises a nucleic acid or     nucleotide sequence according to aspect M-1 or a genetic construct     according to aspect M-2. -   Aspect O-1: Composition comprising at least one amino acid sequence     according to any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8,     D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1, polypeptide according     to any of aspects K-1 to K-18, compound or construct according to     any of aspects L-1 to L-52, monovalent construct according to any of     aspects H-1 or H-3, or nucleic acid or nucleotide sequence according     to aspects M-1 or M-2. -   Aspect O-2: Composition according to aspect O-1, which is a     pharmaceutical composition. -   Aspect O-3: Composition according to aspect O-2, which is a     pharmaceutical composition, that further comprises at least one     pharmaceutically acceptable carrier, diluent or excipient and/or     adjuvant, and that optionally comprises one or more further     pharmaceutically active polypeptides and/or compounds. -   Aspect P-1: Method for producing an amino acid sequence according to     any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32,     E-1 to E-13, F-1 to F-32 or G-1, a polypeptide according to any of     aspects K-1 to K-18, a compound or construct according to any of     aspects L-1 to L-52 that is such that it can be obtained by     expression of a nucleic acid or nucleotide sequence encoding the     same, or a monovalent construct according to any of aspects H-1 or     H-3, said method at least comprising the steps of:     -   a) expressing, in a suitable host cell or host organism or in         another suitable expression system, a nucleic acid or nucleotide         sequence according to aspect M-1, or a genetic construct         according to aspect M-2;     -   optionally followed by:     -   b) isolating and/or purifying the amino acid sequence according         to any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to         D-32, E-1 to E-13, F-1 to F-32 or G-1, a polypeptide according         to any of aspects K-1 to K-18, a compound or construct according         to any of aspects L-1 to L-52, or a monovalent construct         according to any of aspects H-1 or H-3 thus obtained. -   Aspect P-2: Method for producing an amino acid sequence according to     any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32,     E-1 to E-13, F-1 to F-32 or G-1, a polypeptide according to any of     aspects K-1 to K-18, a compound or construct according to any of     aspects L-1 to L-52 that is such that it can be obtained by     expression of a nucleic acid or nucleotide sequence encoding the     same, or a monovalent construct according to any of aspects H-1 or     H-3, said method at least comprising the steps of:     -   a) cultivating and/or maintaining a host or host cell according         to aspect N-1 under conditions that are such that said host or         host cell expresses and/or produces at least one amino acid         sequence according to any of aspects A-1 to A-42, B-1 to B-22,         C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1, a         polypeptide according to any of aspects K-1 to K-18, a compound         or construct according to any of aspects L-1 to L-52, or         monovalent construct according to any of aspects H-1 or H-3;     -   optionally followed by:     -   b) isolating and/or purifying the amino acid sequence according         to any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to         D-32, E-1 to E-13, F-1 to F-32 or G-1, a polypeptide according         to any of aspects K-1 to K-18, a compound or construct according         to any of aspects L-1 to L-52, or monovalent construe according         to any of aspects H-1 or H-3 thus obtained. -   Aspect P-3: Method for preparing and/or generating a bivalent or     multivalent construct according to any of aspects L-8 to L-42, said     method comprising at least the steps of linking two or more     monovalent amino acid sequences or monovalent construct according to     any of aspects H-1 to H-3 and for example one or more linkers. -   Aspect P-4: Method according to aspect P-3, comprising the steps of:     -   a. linking two or more nucleic acid sequences according to         aspect M-1, encoding a monovalent construct according to any of         aspects H-1 to H-3 (and also for example nucleic acids encoding         one or more linkers and further one or more further elements of         genetic constructs known per se) to obtain a genetic construct         according to aspect M-2;     -   b. expressing, in a suitable host cell or host organism or in         another suitable expression system, the genetic construct         obtained in a)     -   optionally followed by:     -   c. isolating and/or purifying the biparatopic or triparatopic         construct according to any of aspects L-8 to L-42 thus obtained. -   Aspect Q-1: Method for screening amino acid sequences directed     against a Target of the invention that comprises at least the steps     of:     -   a) providing a set, collection or library of nucleic acid         sequences encoding amino acid sequences;     -   b) screening said set, collection or library of nucleic acid         sequences for nucleic acid sequences that encode an amino acid         sequence that can bind to and/or has affinity for the Target of         the invention and that is cross-blocked or is cross blocking a         Nanobody of the invention, e.g. SEQ ID NO's: 238 to 253         (Table-1) or SEQ ID NO's: 308 to 311, or a polypeptide or         construct of the invention, e.g. SEQ ID NO: 261 to 266 (see         Table 2); and     -   c) isolating said nucleic acid sequence, followed by expressing         said amino acid sequence. -   Aspect R-1: Method for the prevention and/or treatment of at least     one viral and/or bacterial induced/related disease or disorder, said     method comprising administering, to a subject in need thereof, a     pharmaceutically active amount of at least one amino acid sequence     according to any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8,     D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1, polypeptide according     to any of aspects K-1 to K-18, compound or construct according to     any of aspects L-1 to L-52, monovalent construct according to any of     aspects H-1 or H-3; or composition according to aspect O-2 or O-3. -   Aspect R-2: Method for the prevention and/or treatment of at least     one disease or disorder that is associated with a Target of the     invention, with its biological or pharmacological activity, and/or     with the biological pathways or signalling in which the Target of     the invention is involved, said method comprising administering, to     a subject in need thereof, a pharmaceutically active amount of at     least one amino acid sequence according to any of aspects A-1 to     A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32     or G-1, polypeptide according to any of aspects K-1 to K-18,     compound or construct according to any of aspects L-1 to L-52,     monovalent construct according to any of aspects H-1 or H-3; or     composition according to aspect O-2 or O-3. -   Aspect R-3: Method for the prevention and/or treatment of at least     one disease or disorder that can be prevented and/or treated by     administering, to a subject in need thereof, at least one amino acid     sequence according to any of aspects A-1 to A-42, B-1 to B-22, C-1     to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1, polypeptide     according to any of aspects K-1 to K-18, compound or construct     according to any of aspects L-1 to L-52, monovalent construct     according to any of aspects H-1 or H-3; or composition according to     aspect O-2 or O-3, said method comprising administering, to a     subject in need thereof, a pharmaceutically active amount of at     least one at least one amino acid sequence according to any of     aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to     E-13, F-1 to F-32 or G-1, polypeptide according to any of aspects     K-1 to K-18, compound or construct according to any of aspects L-1     to L-52, monovalent construct according to any of aspects H-1 or     H-3; or composition according to aspect O-2 or O-3. -   Aspect R-4: Method for immunotherapy, said method comprising     administering, to a subject in need thereof, a pharmaceutically     active amount of at least one amino acid sequence according to any     of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to     E-13, F-1 to F-32 or G-1, polypeptide according to any of aspects     K-1 to K-18, compound or construct according to any of aspects L-1     to L-52, monovalent construct according to any of aspects H-1 or     H-3; or composition according to aspect O-2 or O-3. -   Aspect R-5: Use of an amino acid sequence according to any of     aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to     E-13, F-1 to F-32 or G-1, polypeptide according to any of aspects     K-1 to K-18, compound or construct according to any of aspects L-1     to L-52, monovalent construct according to any of aspects H-1 or H-3     in the preparation of a pharmaceutical composition for prevention     and/or treatment of at least one viral or bacterial induced/related     disease or disorder; and/or for use in one or more of the methods     according to aspects R-1 to R-4. -   Aspect R-6: Amino acid sequence according to any of aspects A-1 to     A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32     or G-1, polypeptide according to any of aspects K-1 to K-18,     compound or construct according to any of aspects L-1 to L-52,     monovalent construct according to any of aspects H-1 or H-3; or     composition according to aspect O-2 or O-3 for the prevention and/or     treatment of at least one viral or bacterial induced/related disease     or disorder. -   Aspect R-7: Method of generating an amino acid sequence or single     variable domain according to any of aspects A-1 to A-42, B-1 to     B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1, at     least one building block of compound or construct according to any     of aspects L-8 to L-42, at least one building block of monovalent     construct according to any of aspects H-1 to H-3, comprising at     least the steps of:     -   a. immunizing a Camelid, preferably Llama, with whole cells that         are alive and overexpress the desired extracellular part,         region, domain, loop or other extracellular epitope(s) of one of         the Targets of the invention, e.g. selected from the group         consisting of hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin,         human beta3 integrin, human beta1 integrin, human alpha2         integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9,         on their surface in their native confirmation; and     -   b. selecting for binding for the desired extracellular part,         region, domain, loop or other extracellular epitope(s) using         cell membranes preparation of different (other than the one used         in immunization) cell types overexpressing at least one of the         Targets of the invention, e.g. selected from the group         consisting of hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin,         human beta3 integrin, human beta1 integrin, human alpha2         integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9;         and optionally     -   c. washing only mildly with a buffer such as PBS without         detergents. -   Aspect R-8: Method of screening to identify an amino acid sequence,     e.g. a single variable domain, that is directed against one of the     Targets of the invention, e.g. selected from the group consisting of     hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3     integrin, human beta1 integrin, human alpha2 integrin, hCD81,     hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9, comprising the step     of contacting any of the amino acid sequences or single variable     domains according to any of aspects A-1 to A-42, B-1 to B-22, C-1 to     C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32 or G-1, any of the     compounds or constructs according to any of aspects L-1 to L-52, any     of the monovalent constructs according to any of aspects H-1 to H-3     with one of the Targets of the invention, e.g. selected from the     group consisting of hCD4, hCXCR4, hCCR5, hTLR4, human alphaV     integrin, human beta3 integrin, human beta1 integrin, human alpha2     integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9. -   Aspect S-1: Part or fragment of an amino acid sequence according to     any of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32.     E-1 to E-13, F-1 to F-32 or G-1. -   Aspect S-2: Part or fragment according to aspect S-1, that can     specifically bind to a Target of the invention. -   Aspect S-3: Part of fragment according to any of aspects S-1 or S-2,     that is directed against and/or that specifically binds to one of     the Targets of the invention and that inhibits entry of a virus such     as e.g. HIV, HCV, adenoviruses, hantavirus, herpesvirus, echo-virus     1 and others into cells. -   Aspect S-4: Part of fragment according to any of aspects S-1 or S-2,     that is directed against and/or that specifically binds to one of     the Targets of the invention and wherein the IC50 in the HIV-1     infection assays is equal or below 100 nM, preferably 50 nM, more     preferably 10 nM, even more preferably 1 nM. -   Aspect S-5: Part of fragment according to any of aspects S-1 or S-2,     that is directed against and/or that specifically binds to one of     the Targets of the invention and that has an antiviral activity     (expressed as IC50 measured in the HIV-1 infection assay) equal or     below 100 nM, preferably 50 nM, more preferably 10 nM, even more     preferably 1 nM. -   Aspect S-6: Part of fragment according to any of aspects S-1 or S-2,     that is directed against and/or that specifically binds to one of     the Targets of the invention selected from the group consisting of     hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3     integrin, human beta1 integrin, human alpha2 integrin, hCD81,     hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9 and that inhibits     entry of HIV into cells. -   Aspect S-7: Part of fragment according to any of aspects S-1 or S-2,     that is directed against and/or that specifically binds to one of     the Targets of the invention selected from the group consisting of     hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3     integrin, human beta1 integrin, human alpha2 integrin, hCD81,     hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9 and wherein the IC50     in the HIV-1 infection assays is equal or below 100 nM, preferably     50 nM, more preferably 10 nM, even more preferably 1 nM. -   Aspect S-8: Part of fragment according to any of aspects S-1 or S-2,     that is directed against and/or that specifically binds to one of     the Targets of the invention selected from the group consisting of     hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3     integrin, human beta1 integrin, human alpha2 integrin, hCD81,     hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9 and that has an     antiviral activity (expressed as IC50 measured in the HIV-1     infection assay) equal or below 100 nM, preferably 50 nM, more     preferably 10 nM, even more preferably 1 nM, -   Aspect S-9: Part of fragment according to any of aspects S-1 or S-2,     that is directed against and/or that specifically binds to one of     the Targets of the invention selected from the group consisting of     amino acid sequences with SEQ IDs: 254, 268 to 279 and that inhibits     entry of HIV into cells. -   Aspect S-10: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to one     of the Targets of the invention selected from the group consisting     of amino acid sequences with SEQ IDs: 254, 268 to 279 and wherein     the IC50 in the HIV-1 infection assays is equal or below 100 nM,     preferably 50 nM, more preferably 10 nM, even more preferably 1 nM. -   Aspect S-11: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to one     of the Targets of the invention selected from the group consisting     of amino acid sequences with SEQ IDs: 254, 268 to 279 and that has     an antiviral activity (expressed as IC50 measured in the HIV-1     infection assay) equal or below 100 nM, preferably 50 nM, more     preferably 10 nM, even more preferably 1 nM. -   Aspect S-12: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to to     hCXCR4 (SEQ ID NO: 254) and that inhibits entry of HIV into cells. -   Aspect S-13: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to to     hCXCR4 (SEQ ID NO: 254) and wherein the IC50 in the HIV-1 infection     assays is equal or below 100 nM, preferably 50 nM, more preferably     10 nM, even more preferably 1 nM. -   Aspect S-14: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to to     hCXCR4 (SEQ ID NO: 254) and that has an antiviral activity     (expressed as IC50 measured in the HIV-1 infection assay) equal or     below 100 nM, preferably 50 nM, more preferably 10 nM, even more     preferably 1 nM. -   Aspect S-15: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to one     of the Targets of the invention, e.g. selected from the group     consisting of hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin,     human beta3 integrin, human beta1 integrin, human alpha2 integrin,     hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9. -   Aspect S-16: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to at     least one of the Targets of the invention, e.g. CXCR4, CXCR7 or CD4. -   Aspect S-17: Part of fragment according to aspect S-16, wherein the     member of CXCR4 is human CXCR4. -   Aspect S-18: Part of fragment according to aspect S-16, wherein the     member of CD4 is human CD4. -   Aspect S-19: Part of fragment according to aspect S-16, wherein the     member of CXCR7 is human CXCR7. -   Aspect S-20: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to one     of the Targets of the invention, e.g. selected from the group     consisting of hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin,     human beta3 integrin, human beta1 integrin, human alpha2 integrin,     hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9 and inhibits     and/or blocks binding of the Target of the invention to its ligand. -   Aspect S-21: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to hCD4     and inhibits and/or blocks binding of gp120 to hCD4. -   Aspect S-22: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that specifically binds to     hCXCR4 and inhibits and/or blocks binding of CXCL12 to hCXCR4. -   Aspect S-23: Part of fragment according to any of aspects S-1 or     S-2, that is directed against and/or that a) specifically binds to     one of the Targets of the invention; and b) fully inhibits     ligand-dependent activation of one of the Targets of the invention,     e.g. selected from the group consisting of hCD4, hCXCR4, hCCR5,     hTLR4, human alphaV integrin, human beta3 integrin, human beta1     integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1,     hClaudin-6 and hClaudin-9, wherein the ligand is present in a     concentration of 100 nM or less, more preferably 30 nM or less;     and c) provides no activation of one of the Targets of the     invention. -   Aspect S-24: Part of fragment according to any of aspects S-1 or     S-23, that can specifically bind to a Target of the invention with a     dissociation constant (K_(D)) of 10⁻⁵ to 10⁻¹² moles/litre or less,     and preferably 10⁻⁷ to 10⁻¹² moles/litre or less and more preferably     10⁻⁸ to 10⁻¹² moles/litre. -   Aspect S-25: Part or fragment according to any of aspects S-1 to     S-24, that can specifically bind to a Target of the invention with a     rate of association (k_(on)-rate) of between 10² M⁻¹ s⁻¹ to about     10⁷ M⁻¹s⁻¹, preferably between 10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more     preferably between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, such as between 10⁵     M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹. -   Aspect S-26: Part or fragment according to any of aspects S-1 to     S-25, that can specifically bind to a Target of the invention with a     rate of dissociation (k_(off) rate) between 1 s⁻¹ and 10⁻⁶ s⁻¹     preferably between 10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more preferably between     10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹. -   Aspect S-27: Compound or construct, that comprises or essentially     consists of one or more parts or fragments according to any of     aspects S-1 to S-26, and optionally further comprises one or more     other groups, residues, moieties or binding units, optionally linked     via one or more linkers. -   Aspect S-28: Compound or construct according to aspect S-27, in     which said one or more other groups, residues, moieties or binding     units are amino acid sequences. -   Aspect S-29: Compound or construct according to aspect 5-27 or S-28,     in which said one or more linkers, if present, are one or more amino     acid sequences. -   Aspect S-30: Nucleic acid or nucleotide sequence, that encodes a     part or fragment according to any of aspects S-1 to S-26 or a     compound or construct according to any of aspects S-8 to S-29. -   Aspect S-31: Composition, comprising at least one part or fragment     according to any of aspects S-1 to S-26, compound or construct     according to any of aspects S-27 to S-29, or nucleic acid or     nucleotide sequence according to aspect S-30. -   Aspect T-1: Derivative of an amino acid sequence according to any of     aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to     E-13, F-1 to F-32 or G-1. -   Aspect T-2: Derivative according to aspect T-1, that can     specifically bind to a Target of the invention. -   Aspect T-3: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention and that inhibits entry of a virus such as     e.g. HIV, HCV, adenoviruses, hantavirus, herpesvirus, echo-virus 1     and others into cells. -   Aspect T-4: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention and wherein the IC50 in the HIV-1 infection     assays is equal or below 100 nM, preferably 50 nM, more preferably     10 nM, even more preferably 1 nM. -   Aspect T-5: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention and that has an antiviral activity     (expressed as IC50 measured in the HIV-1 infection assay) equal or     below 100 nM, preferably 50 nM, more preferably 10 nM, even more     preferably 1 nM. -   Aspect T-6: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of hCD4,     hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin,     human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI,     hClaudin-1, hClaudin-6 and hClaudin-9 and that inhibits entry of HIV     into cells. -   Aspect T-7: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of hCD4,     hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin,     human beta1 integrin, human alpha2 integrin, hCD81, hClaudin-1,     hClaudin-6 and hClaudin-9 and wherein the IC50 in the HIV-1     infection assays is equal or below 100 nM, preferably 50 nM, more     preferably 10 nM, even more preferably 1 nM. -   Aspect T-8: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of hCD4,     hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin,     human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI,     hClaudin-1, hClaudin-6 and hClaudin-9 and that has an antiviral     activity (expressed as IC50 measured in the HIV-1 infection assay)     equal or below 100 nM, preferably 50 nM, more preferably 10 nM, even     more preferably 1 nM. -   Aspect T-9: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of amino     acid sequences with SEQ IDs: 254, 268 to 279 and that inhibits entry     of HIV into cells. -   Aspect T-10: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of amino     acid sequences with SEQ IDs: 254, 268 to 279 and wherein the IC50 in     the HIV-1 infection assays is equal or below 100 nM, preferably 50     nM, more preferably 10 nM, even more preferably 1 nM. -   Aspect T-11: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention selected from the group consisting of amino     acid sequences with SEQ IDs: 254, 268 to 279 and that has an     antiviral activity (expressed as IC50 measured in the HIV-1     infection assay) equal or below 100 nM, preferably 50 nM, more     preferably 10 nM, even more preferably 1 nM. -   Aspect T-12: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to to hCXCR4 (SEQ     ID NO: 254) and that inhibits entry of HIV into cells. -   Aspect T-13: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to to hCXCR4 (SEQ     ID NO: 254) and wherein the IC50 in the HIV-1 infection assays is     equal or below 100 nM, preferably 50 nM, more preferably 10 nM, even     more preferably 1 nM. -   Aspect T-14: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to to hCXCR4 (SEQ     ID NO: 254) and that has an antiviral activity (expressed as IC50     measured in the HIV-1 infection assay) equal or below 100 nM,     preferably 50 nM, more preferably 10 nM, even more preferably 1 nM. -   Aspect T-15: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention, e.g. selected from the group consisting of     hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3     integrin, human beta1 integrin, human alpha2 integrin, hCD81,     hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9. -   Aspect T-16: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to at least one     of the Targets of the invention, e.g. CXCR4, CXCR7 or CD4. -   Aspect T-17: Derivative according to aspect T-16, wherein the member     of CXCR4 is human CXCR4. -   Aspect T-18: Derivative according to aspect T-16, wherein the member     of CD4 is human CD4. -   Aspect T-19: Derivative according to aspect T-16, wherein the member     of CXCR7 is human CXCR7. -   Aspect T-20: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to one of the     Targets of the invention, e.g. selected from the group consisting of     hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3     integrin, human beta1 integrin, human alpha2 integrin. hCD81,     hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9 and inhibits and/or     blocks binding of the Target of the invention to its ligand. -   Aspect T-21: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to hCD4 and     inhibits and/or blocks binding of gp120 to hCD4. -   Aspect T-22: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that specifically binds to hCXCR4 and     inhibits and/or blocks binding of CXCL12 to hCXCR4. -   Aspect T-23: Derivative according to any of aspect T-1 or T-2, that     is directed against and/or that a) specifically binds to one of the     Targets of the invention; and b) fully inhibits ligand-dependent     activation of one of the Targets of the invention, e.g. selected     from the group consisting of hCD4, hCXCR4, hTLR4, human alphaV     integrin, human beta3 integrin, human beta1 integrin, human alpha2     integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9,     wherein the ligand is present in a concentration of 100 nM or less,     more preferably 30 nM or less; and c) provides no activation of one     of the Targets of the invention. -   Aspect T-24: Derivative according to any of aspects T-1 or T-23,     that can specifically bind to the Target of the invention with a     dissociation constant (K_(D)) of 10⁻⁵ to 10⁻¹² moles/litre or less,     and preferably 10⁻⁷ to 10⁻¹² moles/litre or less and more preferably     10⁻⁸ to 10⁻¹² moles/litre. -   Aspect T-25: Derivative according to any of aspects T-1 to T-24,     that can specifically bind to the Target of the invention with a     rate of association (k_(on)-rate) of between 10² M⁻¹s⁻¹ to about 10⁷     M⁻¹s⁻¹, preferably between 10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more     preferably between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, such as between 10⁵     M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹. -   Aspect T-26: Derivative according to any of aspects T-1 to T-25,     that can specifically bind to the Target of the invention with a     rate of dissociation (k_(off) rate) between 1 s⁻¹ and 10⁻⁶ s⁻¹     preferably between 10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more preferably between     10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹. -   Aspect T-27: Derivative of a polypeptide according to any of aspects     K-1 to K-18 or compound or construct according to any of aspects L-1     to L-52. -   Aspect T-28: Derivative according to aspect T-27, that can     specifically bind to a Target of the invention. -   Aspect T-29: Derivative according to any of aspects T-27 or T-28,     that can specifically bind to the Target of the invention with a     dissociation constant (K_(D)) of 10⁻⁵ to 10⁻¹² moles/liter or less,     and preferably 10⁻⁷ to 10⁻¹² moles/liter or less and more preferably     10⁻⁸ to 10⁻¹² moles/liter. -   Aspect T-30: Derivative according to any of aspects T-27 to T-29,     that can specifically bind to the Target of the invention with a     rate of association (k_(on)-rate) of between 10² M⁻¹s⁻¹ to about 10⁷     M⁻¹s⁻¹, preferably between 10³ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹, more     preferably between 10⁴ M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹ such as between 10⁵     M⁻¹s⁻¹ and 10⁷ M⁻¹s⁻¹. -   Aspect T-31: Derivative according to any of aspects T-27 to T-30,     that can specifically bind to the Target of the invention with a     rate of dissociation (k_(off) rate) between 1 s⁻¹ and 10⁻⁶ s⁻¹     preferably between 10⁻² s⁻¹ and 10⁻⁶ s⁻¹, more preferably between     10⁻³ s⁻¹ and 10⁻⁶ s⁻¹, such as between 10⁻⁴ s⁻¹ and 10⁻⁶ s⁻¹. -   Aspect T-32: Derivative according to any of aspects T-1 to T-31,     that has a serum half-life that is at least 1.5 times, preferably at     least 2 times, such as at least 5 times, for example at least 10     times or more than 20 times, greater than the half-life of the     corresponding amino acid sequence according to any of aspects A-1 to     A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to E-13, F-1 to F-32     or G-1 per se, polypeptide according to any of aspects K-1 to K-18     or compound or construct according to any of aspects L-1 to L-52 per     se. -   Aspect T-33: Derivative according to any of aspects T-1 to T-132,     that has a serum half-life that is increased with more than 1 hours,     preferably more than 2 hours, more preferably more than 6 hours,     such as more than 12 hours, or even more than 24, 48 or 72 hours,     compared to the corresponding amino acid sequence according to any     of aspects A-1 to A-42, B-1 to B-22, C-1 to C-8, D-1 to D-32, E-1 to     E-13, F-1 to F-32 or G-1 per se, polypeptide according to any of     aspects K-1 to K-18 or compound or construct according to any of     aspects L-1 to L-52 per se. -   Aspect T-34: Derivative according to any of aspects T-1 to T-33,     that has a serum half-life in human of at least about 12 hours,     preferably at least 24 hours, more preferably at least 48 hours,     even more preferably at least 72 hours or more; for example, at     least 5 days (such as about 5 to 10 days), preferably at least 9     days (such as about 9 to 14 days), more preferably at least about 10     days (such as about 10 to 15 days), or at least about 11 days (such     as about 11 to 16 days), more preferably at least about 12 days     (such as about 12 to 18 days or more), or more than 14 days (such as     about 14 to 19 days). -   Aspect T-35: Derivative according to any of aspects T-1 to T-34,     that is a pegylated derivative. -   Aspect T-36: Compound or construct, that comprises or essentially     consists of one or more derivatives according to any of aspects T-1     to T-34, and optionally further comprises one or more other groups,     residues, moieties or binding units, optionally linked via one or     more linkers. -   Aspect T-37: Compound or construct according to aspect T-36, in     which said one or more other groups, residues, moieties or binding     units are amino acid sequences. -   Aspect T-38: Compound or construct according to aspect T-36, in     which said one or more linkers, if present, are one or more amino     acid sequences. -   Aspect T-39: Nucleic acid encoding a compound or construct according     to aspect T-36 or T-37. -   Aspect T-40: Composition, comprising at least one derivative to any     of aspects T-1 to T-35, compound or construct according to any of     aspects T-36 to T-38, or nucleic acid or nucleotide sequence     according to aspect T-39.

EXAMPLES Example 1 Generation of CXCR4 Nanobodies Methods:

Cell culture and transfection—HEK293T cells were maintained at 37° C. in a humidified 5% CO₂, 95% air atmosphere in Dulbecco's modified Eagle's medium (DMEM) containing 2 mM L-glutamine, 50 IU/ml penicillin, 50 μg/ml streptomycin, and 10% (v/v) fetal calf serum. Jurkat cells were cultured in a humidified 5% CO₂, 95% air atmosphere in a 1:1 mixture of Dulbecco's modified Eagle's medium (DMEM) and Ham's F12 medium containing 2 mM L-glutamine, 50 IU/ml penicillin, 50 μg/ml streptomycin, and 10% (v/v) fetal calf serum. HEK293T cells were transiently transfected with a constant amount of total DNA using linear 25 kDa polyethyleneimine (Polysciences, Warrington, Pa.) as carrier as previously described (Verzijl et al., Noncompetitive Antagonism and inverse Agonism as Mechanism of Action of Nonpeptidergic Antagonists at Primate and Rodent CXCR3 Chemokine Receptors. Journal of Pharmacology and Experimental Therapeutics (2008) 325(2):544-55). cDNA encoding chemokine receptors CCR5, CCR7, CXCR1, CXCR2, CXCR3 and CXCR7 obtained from cdna.org (Missouri S&T cDNA Resource Center, Rolla, Mo.) were amplified by PCR and cloned into an expression vector.

[¹²⁵I]-labelling—Radiolabeling of Nanobodies with ¹²⁵I was performed using the Iodo-gen method (Pierce, Rockford, Ill.) according to the manufacturer's protocol. ¹²⁵I-labeled Nanobody was separated from free iodine (>99%) using a Sephadex G-25 gel filtration column (Amersham Biosciences, Piscataway, N.J.). Iodine incorporation and specific activity were controlled via precipitation of the protein with trichloroacetic acid. myo-[2-³H]-inositol (10-20 Ci/mmol) and [¹²⁵I]-labeled CXCL12 (2,200 Ci/mmol) were obtained from PerkinElmer Life and Analytical Sciences (Boston, Mass.).

Competition binding assays—Membranes from HEK293T cells transiently expressing CXCR3 or CXCR4 were prepared 48 h after transfection as follows. Cells were washed and scraped from the cell culture dishes with ice-cold PBS containing 1 mm EDTA. The scraped cells were pelleted at 1500×g for 10 min at 4° C. The pellet was washed and then resuspended in ice-cold membrane buffer (15 mM Tris, pH 7.5, 1 mM EGTA, 0.3 mM EDTA, and 2 mM MgCl₂). The cell suspension was homogenized by 10 strokes at 1200 rpm using a Teflon-glass homogenizer and rotor and further subjected to three freeze-thaw cycles using liquid nitrogen. Membranes were separated by centrifugation at 40,000 g for 25 min at 4° C. The membrane pellet was washed and resuspended in ice-cold Tris-sucrose buffer (20 mM Tris, pH 7.4, and 250 mM sucrose) and frozen in liquid nitrogen. The total protein was determined using a Bradford assay (Bio-Rad).

Periplasmas (1:10) or ligands were pre-incubated with membranes in binding buffer (50 mM HEPES (pH 7.4), 1 mM CaCl₂, 5 mM MgCl₂, 100 mM NaCl, 0.5% bovine serum albumin) supplemented with 0.5% BSA for 1 h at 22° C. before the addition of [¹²⁵I]-CXCL12 (40 pM) or [¹²⁵I]-238D2 (3 nM) or [¹²⁵I]-238D4 (3 nM) for additional 2 h at 22° C. The non-specific binding was determined in the presence of AMD3100 (3 μM). Membranes were then harvested over polyethylenimine (0.5%)-treated. Whatman GF/C filter plates and washed three times with ice cold binding buffer containing 500 mM NaCl. Plates were counted by liquid scintillation.

Inositol phosphate accumulation assay—24 hours post transfection with pcDNA3.1-CXCR4 and pcDNA1-HA-mG {alpha} qi5 (see Verzijl et al, 2008 supra), 250.000 cells were seeded into 24-wells plates and labelled overnight using inositol-free minimal essential medium supplemented with 1 μCi myo-[2-³H]-inositol. The next day, the cells were washed once to remove not incorporated myo-[2-³H]-inositol. In antagonist experiments, the cells were pre-incubated with test compounds at 37° C. in assay medium (20 mM HEPES, 140 mM NaCl, 5 mM KCl, 1 mM MgSO₄, 1 mM CaCl₂, 10 mM glucose and 0.05% (w/v) bovine serum albumin, pH 7.4) for 1 h before stimulation with LiCl (10 mM) and CXCL12 (30 nM) for further 2 h at 37° C. In agonist experiments, the cells were directly stimulated with test compounds and LiCl (10 mM) in assay buffer for 2 h at 37° C. The stimulation was stopped by aspirating the stimulation medium and adding ice-cold 10 mM formic acid. The accumulated inositol phosphates were isolated by anion exchange chromatography and counted by liquid scintillation.

CRE reporter gene assay—HEK239T cells were transfected with pCRE/β-galactosidase (Chen W, Shields T S, Stork R N, Cone R D (1995) Anal Biochem 226:349-354) and plasmids (pcDEF₃ or pcDNA3.1) encoding the indicated receptors. 40,000 transfected cells per well were seeded into 96 well plates and grown in DMEM supplemented with 10% fetal calf serum. The medium was replaced 32 h after transfection by serum-free DMEM supplemented with 0.5% bovine serum albumin and ligands as indicated. Following 16 h of ligand incubation, the medium was removed, the cells were lysed in 100 μl of assay buffer (100 mM sodium phosphate buffer at pH 8.0, 4 mM 2-nitrophenol-β-D-pyranoside, 0.5% Triton X-100, 2 mM MgSO₄, 0.1 mM MnCl₂, and 40 mM β-mercaptoethanol) and incubated at room temperature. The β-galactosidase activity was determined by the measurement of absorption at 420 nm with a PowerwaveX340 plate reader (Bio-Tek Instruments Inc., Winooski, Vt.) after incubation with the assay buffer when the OD₄₂₀ value for forskolin (3 μM) controls reached 0.4-0.6.

Chemotaxis assay—The chemotactic responsiveness of Jurkat 3D cells was assessed using ChemoTx™ plates (Receptor Technologies Ltd., Oxon, UK) in which a upper cell-containing compartment is separated from a lower chemoattractant-containing compartment by a polyvinylpyrollidone-free polycarbonate filter with 5-μm pores. Cells were harvested, washed and resuspended in RPMI containing 0.5% bovine serum albumin and then loaded to 150,000 cells per well in a volume of 25 μl into the upper compartment of the chemotaxis chamber. To stimulate cells migrating through the membrane, CXCL12 and/or test compounds were loaded in a final volume of 31 μl at indicated concentrations into the lower compartment (agonist experiments). For the characterization of antagonistic properties, AMD3100 or test compounds were loaded to the lower CXCL12 (300 pM) containing compartment and additionally pre-incubated with the cells in the upper compartment. The chemotaxis chambers were incubated at 37° C., 100% humidity, and 5% CO₂ for 4 h. The number of cells migrating into each lower compartment was determined by fluorescence measurement at 535 nm following incubation with calcein AM and calibration with 0 to 50,000 Jurkat 3D cells per well.

HIV-1 infection assays—The CXCR4-using (X4) HIV-1 molecular clone NL4.3 was obtained from the National Institutes of Health NIAID AIDS Reagent program (Bethesda, Md.), the CCR5-using (R5) HIV-1 strain BaL was obtained from the Medical Research Council AIDS reagent project (Herts, UK). The dual-tropic (R5/X4) HIV-1 HE strain was initially isolated from a patient at the University Hospital in Leuven, and had been routinely cultured in MT-4 cells (Pauwels R, Andries K, Desmyter J, Schols D, Kukla M J, Breslin H J, Raeymaeckers A, Van Gelder J, Woestenborghs R, Heykants J. Potent and selective inhibition of HIV-1 replication in vitro by a novel series of TIBO derivatives. Nature 1990; 343:470-474). The MT-4 cells were seeded out in 96-well plate and the U87 cells in 24-well plates. The test compounds were added at different concentrations together with HIV-1 and the plates were maintained at 37° C. in 10% CO₂. Cytopathic effect induced by the virus was monitored by daily microscopic evaluation of the virus-infected cell cultures. At day 4-5 after infection, when strong cytopathic effect was observed in the positive control (i.e., untreated HIV-infected cells), the cell viability was assessed via the in situ reduction of the tetrazolium compound MTS, using the CellTiter 96® AQ_(ueous) One Solution Cell Proliferation Assay (Promega, Madison, Wis.). The absorbance was then measured spectrophotometrically at 490 nm with a 96-well plate reader (Molecular Devices, Sunnyvale, Calif.) and compared with four cell control replicates (cells without virus and drugs) and four virus control wells (virus-infected cells without drugs). The 50% inhibitory concentration (IC₅₀, i.e. the drug concentration that inhibits HIV-induced cell death by 50%), was calculated for each compound from the dose-response curve. The CC₅₀ or 50% cytotoxic concentration of each of the compounds was determined from the reduction of viability of uninfected cells exposed to the agents, as measured by the MTS method described above.

Peripheral blood mononuclear cells (PBMCs) from healthy donors were isolated by density centrifugation (Lymphoprep; Nycomed Pharma, AS Diagnostics, Oslo, Norway) and stimulated with phytohemagglutin (PHA) (Sigma Chemical Co., Bomem Belgium) for 3 days. The activated cells (PHA-stimulated blasts) were washed with PBS and viral infections were performed as described previously (Schols D, Struyf S, Van Damme J, Este S A, Henson G, De Clercq E. Inhibition of T-tropic HIV strains by selective antagonization of the chemokine receptor CXCR4. J Exp Med 1997; 186:1383-1388). At 8-10 days after the start of the infection, viral p24 Ag was detected in the culture supernatant by an enzyme-linked immunosorbent assay (Perkin Elmer, Brussels, Belgium).

Data analysis and presentation—Data are presented as mean±S.E.M. from n independent experiments. Concentration response curves (E/[A] curves) were fitted to the Hill equation using an iterative, least-squares method (GraphPad Prism 4.0, GraphPad Software, San Diego, Calif.) to provide maximal inhibitory effects (I_(max)), half maximal effective (EC₅₀) or inhibitory concentrations (IC₅₀). Competition binding affinities and functional antagonist affinities (pK_(i)) were calculated using the Cheng and Prusoff equation pK_(i)=IC₅₀/(1+[agonist]/EC₅₀) (Cheng & Prusoff, 1973). Antagonist affinities were optionally expressed as pK_(B) values using the method of Arunlakshana and Schild (1959) based on the equation pK_(B)=−log [antagonist]+log(CR-1) where CR represents the ratio of the agonist EC₅₀ in the presence and the absence of an antagonist.

Results were compared using Student's t-test or oneway analysis of variance followed by Bonferroni corrected t-test for stepwise comparison, when multiple comparison was made. P values <0.05 were considered to be significant.

Sequence targets—Synonyms: CXCR-4/Stromal cell-derived factor 1 receptor (SDF-1 receptor)/Fusin/Leukocyte-derived seven transmembrane domain receptor (LESTR)/LCR1/FB22/NPYRL/HM89/CD184 antigen. Human CXCR4 was used for selection:

TABLE B-1 HOMOLOGY AGAINST HUMAN SEQUENCE: 95% WITH MACACA, 92% PIG, 93% DOG, 91% RABBIT, 88% MOUSE, 80% CHICK Amino acid sequence Clone name SEQ ID NO: MEGISSIPLPLLQIYTSDNYTEEMGSGDYDSMKEPCFRFENANFN HUMAN 254 KIFLPTIYSIIFLTGIVGNGLVILVMGYQKKLRSMTDKYRLHLSV gi|3059120|emb| ADLLFVITLPFWAVDAVANWYFGNFLCKAVHVIYTVNLYSSVLIL CAA12166.1|CXCR4 AFISLDRYLAIVHATNSQRPRKLLAEKVVYVGVWIPALLLTIPDF [Homo sapiens] IFANVSEADDRYICDRFYPNDLWVVVFQFQHIMVGLILPGIVILS CYCIIISKLSHSKGHQKRKALKTTVILILAFFACWLPYYIGISID SFILLEIIKQGCEFENTVHKWISITEALAFFHCCLNPILYAFLGA KFKTSAQHALTSVSRGSSLKILSKGKRGGHSSVSTESESSSFHSS IYTSDNYTEEMGSGDYDSIKEPCFREENAHFNRIFLPTIYSIIFL MACACA6 255 TGIVGNGLVILVMGYQKKLRSMTDKYRLHLSVADLLFVITLPFWA gi|9587708|gb| VDAVANWYFGNFLCKAVHVIYTVNLYSSVLILAFISLDRYLAIVH AAF89346.1| ATNSQKPRKLLAEKVVYVGVWIPALLLTIPDFIFASVSEADDRYI AF172226_1 chemokine CDRFYPNDLWVVVFQFQHIMVGLILPGIVILSCYCIIISKLSHSK receptor CXCR4 GHQKRKALKTTVILILAFFACWLPYYTGISIDSFILLEIIKQGCE [Macaca FENTVHKWISITEALAFFHCCLNPILYAFLGAKFKTSAQHALTSV nemestrina] SRGSSLKILSKGKRGGHSSVSTESESSSFHSS MEELHIYPSDNYTEEDLGSGDYDSMKEPCFREENAHFNRIFLPTV DOG 256 YSIIFLTGIVGNGLVILVMGYQKKLRSMTDKYRLHLSVADLLFVL gi|114149257|sp| TLPFWAVEAVANWYFGNFLCKAVHVIYIVNLYSSVLILAFISLDR Q3LSL6.1|CXCR4_ YLAIVHATNSQRPRKLLAEKVVYVGVWIPALLLTIPDFIFANVRE CANFA C-X-C ADDRYICDRFYPNDSWLVVFQFQHIMVGLILPGIVILSCYCIIIS chemokine KLSHSKGYQKRKALKTTVILILAFFACWLPYYIGISIDSFILLEI receptor type 4 IKQGCEFEKTVHKWISITEALAFFHCCLNPILYAFLGAKFKTSAQ (CXC-R4) (CXCR-4) HALTSVSRGSSLKILSKGKRGGHSSVSTESESSSFHSS (CD184 antigen) MDGFRIFTSDNYTEDDLGSGDYDSIKEPCFREENAHFNRIFLPTV PIG 257 YSIIFLTGIVGNGLVILVMGYQKKLRSMTDKYRLHLSVADLLFVL gi|71493324|gb| TLPFWAVDAVANWYFGKFLCKAVHVIYTVNLYSSVLILAFISLDR AAZ32767.1|CXCR4 YLAIVHATNSQRPRKLLAEKVVYVGVWIPALLLTIPDFIFANVRE [Sus scrofa] GDGRYICDRFYPNDLWLVVFQFQHIMVGLILPGIVILSCYCIIIS KLSHSKGYQKRKALKTTVILILAFFACWLPYYIGISIDSFILLEI IQQGCEFESTVHKWISITEALAFFHCCLNPILYAFLGAKFHTSAQ HALTSVSRGSSLKILSKGKRGGHSSVSTESESSSFHSS MDGLDLSSGILIEFADNGSEEIGSADYGDYGEPCFQHENADFNRI CHICK 258 FLPTIYSIIFLTGIIGNGLVIIVMGYQKKQRSMTDKYRLHLSVAD gi|9954428|gb| LLFVITLPFWSVDAAISWYFGNVLCKAVHVIYTVNLYSSVLILAF AAG09054.1| ISLDRYLAIVHATNSQRPRKLLAEKIVYVGVWLPAVLLTVPDIIF AF294794_1 chemokine ASTSEVEGRYLCDRMYPHDNWLISFRFQHILVGLVLPGLIILTCY receptor CXCR4 CIIISKLSHSKGHQKRKALKTTVILILTFFACWLPYYIGISIDTF [Gallus gallus] ILLGVIRHRCSLDTIVHKWISITEALAFFHCCLNPILYAFLGAKF KTSAQNALTSVSRGSSLKILSKSKRGGHSSVSTESESSSFHSS TSDNYTEELGSGDYDSIKEPCFREENAHFNRIFLPTIYSIIFLTG RABBIT 259 IVGNGLVILVMGYQKKQRSMTDKYRLHLSVADLLFVITLPFWAVD gi|161177115|gb| AVANWYFGKFLCKAVHVIYTVNLYSSVLILAFISLDRYLAIVHAT ABX59689.1| NSQKPRKLLAEKVVYVGVWIPALLLTIPDFIFANVREAEGRYICD chemokine RFYPSDLWVVVFQFQHIMVGLILPGIVILSCYCIIISKLSHSKGH receptor CXCR4 QKRKALKTTVILILAFFACWLPYYIGISIDSFILLEIIKQGCEFE [Oryctolagus NTVHKWISITEALAFFHCCLNPILYAFLGAKFKTSAQHALTSVSR cuniculus] GSSLKILSKGKRGGHSSVSTESES MEPTSVSIYTSDNYSEEVGSGDYDSNKEPCFRDENVHFNRIFLPT MOUSE1 260 IYFIIFLTGIVGNGLVILVMGYQKKLRSMTDKYRLHLSVADLLFV gi|2494970|sp| ITLPFWAVDAMADWYFGKFLCKAVHIIYTVNLYSSVLILAFISLD P70658.2|CXCR4_MOUSE RYLAIVHATNSQRPRKLLAEKAVYVGVWIPALLLTIPDFIFADVS C-X-C chemokine QGDISQGDDRYICDRLYPDSLWMVVFQFQHIMVGLILPGIVILSC receptor type 4 YCIIISKLSHSKGHQKRKALKTTVILILAFFACWLPYYVGISIDS (CXC-R4) (CXCR-4) FILLGVIKQGCDFESIVHKWISITEALAFFHCCLNPILYAFLGAK (Stromal cell- FKSSAQHALNSMSRGSSLKILSKGKRGGHSSVSTESESSSFHSS derived factor 1 receptor) (SDF-1 receptor) (Fusin) (Leukocyte- derived seven transmembrane domain receptor) (LESTR) (Pre-B- cell-derived chemokine receptor) (PB- CKR) (CD184 antigen)

TABLE B-1.2 SEQUENCES SELECTED NANOBODIES: Amino Acid Sequence Clone name SEQ ID NO: EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAP 238C1, 238D2 238 GKGLEWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQ MYSLKPEDTAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSS EVQLMESGGGLVQAGGSLRLSCAASGRTFNNYAMGWFRRAP 238D4, 238G3 239 GKEREFVAAITRSGVRSGVSAIYGDSVKDRFTISRDNAKNT LYLQMNSLKPEDTAVYTCAASAIGSGALRRFEYDYSGQGTQ VTVSS KVQLVESGGGLVQPGGSLRLSCAASGFAFSIHTMSWVRQAP 237B5 240 KRGPEWVSTIKPSGDTTNYANAVKGRFTISRDNAKNTLYLQ MNSLKPEDTAVYYCAKDYFGTGVRGQGTQVTVSS EVQLVESGGGLVQPGGSLRLSCAASGFTFDDYAMSWVRQAP 237B6, 237A5, 241 GKGLEWVSAISWNGGSTDYADSVKGRFTISRDNAKNTLYLQ 237D2, 237D3, MNSLKSEDTAEYYCARDQGPFYSGTYYTTRQYGYRGQGTQV 237E4, 237F4, TVSS 237G2, 237G4, 237xH5, 237F1, 237C5, 237G1 EVQLVESGGGFVQAGGSLRLSCETSGRPLLGYTIAWFRQVP 238B10 242 GKEREFVAYHRWSDGANLYADSVKGRFTISGHNAKNTVSLQ MNSLKPEDTAVYYCAAARMTTSNDKEYLYWGQGTQVTVSS EVQLVESGGGFVQAGGSLRLSCETSGRPLLGYTIAWFRQVP 238F7 244 GKEREFVAYHRWSDGANLYADSVKGRFTISGHNAKNTVSLQ MNSLKPEDTAVYYCAAWMTTSNDKEYLYWGQGTQTVSS EVQLVESGGGLVQAGGSLRLSCAASGLTFSPSAMAWYRQGP 238H2 245 GKERDFVASTIWSRGDTYFADSVKGRFTISRDTANYTLYLQ MNNLKPEDTAVYYCSLRVRPYGQYDYWGQGTQVTVSS EVQLVESGGGLVQPGGSLRLSCAASGFTFDDYAMSWVRQAP 237D4 246 GKGLEWVSAISWNGGSADYADSVKGRFTISRDNAKNTLYLQ MNSLKSEDTAVYYCAKDQGPFYSGTYYYTKGYAYWGQGTQV TVSS EVQLVESGGCLAQAGGSLRLSCAASGRTYAMGWFRQAPGKE 238F3 247 REFVTTSRLITDNIIYADSVKGRFTLTRDNGKNTVYLQMDS LKPDDTAVYFCAARQNYSRSVFGAKDYDYWGQGTQVTVSS EVQLVESGGGLVQAGGSLRLSCAASGSIFSLNAMGWYRQAP 237A6 248 GKQRELVAGITSSTSTYYADSVKGRFTISRDNTKNTVYLQM NSLKPEDTAVYYCNVDCPDYYSDYECPLEDRGQGTQVTVSS EVQLVESGGGLAQPGGPLRLTCEASGVIYSVNDMGWYRQAP 237D1 249 GKQRELVAVITSGGGTNYVDSVKGRFTISGDNRKKTVYLQM NSLKPEDTAVYYCSIYYSSGISTLRSWGQGTQVTVSS EVQLVESGGGLVQPGGSLRLSCEVSGFTRDYYTIGWFRQAP 237E1 250 GKEREGVSCISSSDGSTAYLGSVQGRFTVSRDNAKNTVYLQ MNNLKPEDTAVYYCALBSADSRCSIGSIGFTWLYNNWGQGT QVTVSS EVQLVESGGGLVQPGGSLRLSCLASSFIGNYHAIVWLRQAP 237G7 251 GKELEGVSCITSRDSITYYASFVKGRFTISRDDAKNTVYLQ MNNLKPEDTAVYYCAVBTSMTCPTLIVRFNYRGQGTQVTVS S EVQLVESGGGLVQAGGSLRLSCKASGGTFNNYANGWFRRAP 238C4 252 GKEREFVAAITRSGVRSGVSAIYGDSVKDRFTISRDNVKNT LYLQMNTLKPEDTAVYTCAASAIGSGALRRFEYDYSGQGTQ VTVSS EVQLVESGGGLVQAGGSLRLSCAASGSFFSINAMGWYRQAP 237C1 253 GKQRELVASITSGGSTVYADSVKGRFTISRDNYNTVYLQMN SLKPEDTAVYYCNADGVPEWGKVQYPDTYRGQGTQVTVSS EVQLMESGGGLVQAGGSLRLACAASGFTFEDYAIGWFRKAP 238C5, 238G2, 243 GKEREGVSCISGSDGSTTYADSVKGRFTISTDNAKNTVYLE 238xH5, 238C3, MNSLKPEDTAVYYCAQQYGVGGRVVCPGPYEYDVWGQGTQV 238D6, 238E6 TVSS EVQLVESGGGLVQSGGSLRLSCAASGFTFSGYWMYWVRQAP 01B6 308 GKGLEWVSAISPGGGSTYYPDSVKGRFTISRDNAKNTLYLQ MNSLKPEDTALYYCASSLTATHTYEYDYWGQGTQVTVSS EVQLVESGGGLVQAGGSLRLSCAASCRTSASYSMGWFRQAP 01E2 309 GKEREFVAAISWSGDETSYADSVKGRFTTARGNAKNTVYLQ MNSLKSEDTAIYYCAGDRWWRPAGLQWDYWGQGTQVTVSS EVQLVESGGGLVQAGGSLKLSCAASRSILDFNAMGWYRQAP 01H12 310 GKQREWVTTIARAGATKYADSVKGRFSISRDNAKNTVYLQM SSLKPEDTATYYCNARVFDLPNDYWGQGTQVTVSS EVQLVESGGGSVQPGGSLTLSCGTSGRTFNVMGWFRQAPGK 03F11 311 EREFVAAVRWSSTGIYYTQYADSVKSRFTISRDNAENTVYL EMNSLKPEDTAVYYCAADTYNSNPARWDGYDFRGQGTQVTV SS

Example 1.1 Immunizations

For immunization, HEK293 cells (human embryonic kidney) transiently expressing human CXCR4 were used as “antigen”. Two llamas were immunized according to standard protocols with 6 boosts of a cells (1*10E7 cells) at day 0, 7, 21, 32, 43 and 56. Blood were collected from these animals at 4 and 8 days after the 6^(th) boost.

Example 1.2 Library Construction

Peripheral blood mononuclear cells were prepared from blood samples using Ficoll-Hypaque according to the manufacturer's instructions. Next, total RNA extracted was extracted from these cells as well as from the lymph node bow cells and used as starting material for RT-PCR to amplify Nanobody encoding gene fragments. These fragments were cloned into a phagemid vector. Phage was prepared according to standard methods (see for example the prior art and applications filed by applicant cited herein) and stored at 4° C. for further use, making phage library 217 and 218.

Example 1.3 Selections Using 2 Rounds of Trypsine Elution

To identify Nanobodies recognizing CXCR4, phage libraries (217, 218) were used in a phage display selection.

Because hCXCR4 is an integral transmembrane protein, it is essential to conserve the native conformation of hCXCR4. Therefore, the phage display selection was done on cell membranes preparation of CHO and COS7 cells overexpressing hCXCR4. Membranes were coated onto Maxisorp plate overnight at 4° C. (10 ug in 100 ul PBS). The next day, after blocking in 4% milk-PBS 1 hour, phages from the libraries were incubated with the coated membrane in the presence (and in parallel without) of 1% milk-PBS and CHO-membrane preparation expressing a non-relevant membrane protein. After 2 hours incubation, the plates were washed extensively with PBS. After washing, bound phages were eluted using trypsine (1 ug/ml) for 15 min at RT. Phages were rescued and reamplified in TG1 as usual giving R1 polyclonal phages.

Those R1 phages were used for a second round of selection like the first round with the only difference that phages selected on CHO-CXCR4 membrane in the first round were also used on COS7-CXCR4 membrane and reverse. This unique strategy allows the depletion on non-CXCR4 specific phages. After 2 hours incubation, the plates were washed extensively with PBS and bound phages were eluted using trypsine (1 ug/ml) for 15 min at RT.

Output of R2 selections were analyzed for enrichment factor (phage present in eluate relative to controls). Based on these parameters the best selections were chosen for further analysis. The polyclonal output was rescued in TG1, individual TG1 colonies were picked and grown in 96 deep well plates (1 ml volume) to produce monoclonal phages (addition of helper phage) or monoclonal periplasmic Nanobody fractions (addition of IPTG). Periplasmic extracts (volume: ˜90 ul) were prepared according to standard methods (see for example the prior art and applications filed by applicant cited herein).

A schematic representation of the selection can be found in FIG. 1.

Example 1.4 Selections Using 2 Rounds of Specific (Competitive) Elution

An alternative to the non-specific trypsine elution is to use specific CXCR4 binding compound to elute (compete out) the phages binding to the site of the compound binding. In this case, 2.5 ug of membrane preparation was coated overnight at 4 C in 100 ul PBS and elution was done for 30 min at RT with an excess of:

-   -   CXCL12/SDF1 (3 ug in 100 ul PBS), the natural ligand for CXCR4,     -   AMD3100 (50 uM), a know chemical antagonist (from Sigma Aldrich)     -   12G5 (5 ug in 100 ul PBS), a known neutralizing antibody (from         R&D System). Eluted phages were rescued and reamplified in TG1         as usual giving R1 polyclonal phages.

Those R1 phages were used for a second round of selection like the first round with the only difference that phages selected on CHO-CXCR4 membrane in the first round were also used on COS7-CXCR4 membrane and reverse. This unique strategy allows the depletion on non-CXCR4 specific phages (membrane specific). After 2 hours incubation, the plates were washed extensively with PBS and bound phages were eluted as the first round. This way, 2 rounds of CXCL12/SDF1 was done as well as 2 rounds of AMD3100.

Output of R2 selections were analyzed for enrichment factor (phage present in eluate relative to controls). Based on these parameters the best selections were chosen for further analysis. The polyclonal output was rescued in TG1, individual TG1 colonies were picked and grown in 96 deep well plates (1 ml volume) to produce monoclonal phages (addition of helper phage) or monoclonal periplasmic Nanobody fractions (addition of IPTG). Periplasmic extracts (volume: ˜90 ul) were prepared according to standard methods (see for example the prior art and applications filed by applicant cited herein).

A schematic representation of the selection can be found in FIG. 1.

Example 1.5 Screening for Binding

In order to determine binding specificity of the Nanobodies, 15 ul of the produced phage were tested in an Phage ELISA binding assay.

In short, 2 ug in 100 ul PBS of membrane expressing either CXCR4 (CHO-CXCR4) or a non relevant GPCR (CHO) were coated directly on maxisorop microtiter plates (Nunc) overnight at 4 C. Free binding sites were blocked using 4% Marvel in PBS for 1 h. Next, 15 ul of monoclonal phages was added in 100 ul 1% Marvel PBS for 2 hours. After incubation and a extensive PBS washing step, phage binding was revealed using an anti-M13-HRPO antibody. Binding specificity (binding to CHO-CXCR4) was determined based on OD values compared to controls (binding to CHO).

An example is shown in FIG. 2.

Example 1.6 Screening of CXCR4-Binding Nanobodies by Displacement of [¹²⁵I]-CXCL12

180 clones were analyzed and their periplasma fractions were screened using a CXCR4 competition binding assay. In a primary screen with membranes from HEK293T cells transiently expressing CXCR4, approximately 13% of the clones were found to compete with the radiolabeled endogenous CXCR4 ligand [¹²⁵I]-CXCL12 for binding to CXCR4 and produce an inhibition of specific [¹²⁵I]-CXCL12 binding of at least 30% (FIG. 3). A total amount of five clones (approximately 3%) strongly inhibit specific [¹²⁵I]-CXCL12 binding by more than 70%. No inhibition was observed for control phages expressing Nanobodies directed against membrane proteins different from CXCR4.

All primary hits were confirmed in a second screen (FIG. 3 b) and therefore the V_(H)H-encoding DNA of CXCL12-displacing Nanobody-producing clones were sequenced. Sequencing analysis results in seven pools of identical or highly similar clones strongly (2 pools) or partially (5 pools) displacing [¹²⁵I]-CXCL12 (Table B-2). Nanobodies representing these pools, namely 237A6, 237D1, 237D2, 237G7, 238C5, 238D2 and 238D4 were purified and further pharmacologically analyzed.

Characterization of Nanobody binding to CXCR4—Following purification, receptor binding characteristics for 237A6, 237D1, 237D2, 237G7, 238C5, 238D2 and 238D4 were investigated on cell membranes from transiently CXCR4 expressing HEK293T cells. The Nanobodies 238D2 and 238D4 fully displace all specifically bound [¹²⁵I]-CXCL12 and show affinities to CXCR4 in the low nanomolar range (Table B2). All other Nanobodies were unable to displace [¹²⁵I]-CXCL12 even at the highest test concentration of 0.5 μM (237A6, 237D1, 237D2, 237G7 and 238C5) (FIG. 4A; Table B-3).

In order to further investigate the binding properties of the two potently [¹²⁵I]-CXCL12-displacing Nanobodies 238D2 and 238D4 to CXCR4, we generated ¹²⁵I-labeled Nanobodies for competition binding studies. Both, [¹²⁵I]-238D2 and [¹²⁵I]-238D4 selectively bound to membranes from HEK293T cells transiently expressing CXCR4 compared to those expressing CXCR3 (FIG. 4D). Both Nanobodies compete for binding to CXCR4 as shown by the full displacement of [¹²⁵I]-238D2 by 238D4 and by the full inhibition of [¹²⁵I]-238D4 binding by 238D2 (FIGS. 4B, 4C). Furthermore, the small molecule ligand AMD3100 displaced [¹²⁵I]-238D2 and [¹²⁵I]-238D4 with affinities comparable to those obtained against [¹²⁵I]-CXCL12 (Table B-3) indicating that also AMD3100 compete with the Nanobodies 238D2 and 238D4 for the same receptor. The monoclonal antibody 12G5 that has previously been reported to label a certain subpopulation of CXCR4 (J. Virol. Baribaud et at 75 (19): 8957) potently but incompletely displace specifically bound [¹²⁵I]-CXCL12, [¹²⁵I]-238D2 and [¹²⁵I]-238D4 from CXCR4. 237A6, 237D1, 237D2 and 237G7 were unable to inhibit binding of [¹²⁵I]-238D2 or [¹²⁵I]-238D4 to CXCR4. 238C5 displaced [¹²⁵I]-238D2 and [¹²⁵I]-238D4 but not [¹²⁵I]-CXCL12 at high concentrations (>100 nM) indicating that this Nanobody binds to the receptor as a low affinity allosteric CXCR4 ligand (FIGS. 4B, 4C).

TABLE B-2 Screening and sequencing of Nanobody clones displacing [¹²⁵I]-CXCL12. Binding efficiency was determined by competition binding with [¹²⁵I]-CXCL12 on membranes from HEK293T cells transiently expressing CXCR4. Pool Clones Binding^(a) 237A6 237A6 + 237D1 237D1 + 237D2 237B6, 237C1, 237C5, 237D2, 237D4, −/+ 237E4, 237F4, 237H1, 237G1 237G4, 237H5 237G7 237G7 + 238C5 238C5, 238D6, 238E6 + 238D2 238C1, 238D2 ++ 238D4 238C4, 238D4, 238G3 ++ ^(a)− = 0-29%; + = 30-69%; ++ = 70-100%.

TABLE B-3 Receptor affinity (pK_(i)) and maximal displacement of [¹²⁵I]-CXCL12, [¹²⁵I]-238D2 and [¹²⁵I]-238D4 for monovalent Nanobodies and CXCR4 reference ligands. [¹²⁵I]-CXCL12 [¹²⁵I]-238D2 [¹²⁵I]-238D4 Displacem. Displacem. Displacem. (%) pK_(i) n (%) pK_(i) n (%) pK_(i) n 238D2 93 ± 5 8.01 ± 0.12 6 97 ± 6 8.41 ± 0.11 4 105 ± 4 8.23 ± 0.23 4 238D4 99 ± 5 8.22 ± 0.16 6 101 ± 1  8.80 ± 0.23 4 103 ± 1 8.55 ± 0.09 4 237A6 0^(a) <6.3 4 0^(a) <6.3 2 0^(a) <6.3 2 237D1 0^(a) <6.3 3 0^(a) <6.3 2 0^(a) <6.3 2 237D2 0^(a) <6.3 4 0^(a) <6.3 2 0^(a) <6.3 2 237G7 0^(a) <6.3 4 0^(a) <6.3 2 0^(a) <6.3 2 238C5 0^(a) <6.3 4  45 ± 5^(b) <7.0 3   38 ± 4^(b) <7.0 3 116B2 0^(a) <6.3 2 0^(a) <6.3 2 0^(a) <6.3 2 CXCL12 105 ± 2  9.84 ± 0.13 3 98 ± 8 7.46 ± 0.17 4  93 ± 2 7.45 ± 0.12 4 AMD3100 94 ± 2 7.41 ± 0.28 3 102 ± 1  7.74 ± 0.19 4  99 ± 4 7.34 ± 0.16 4 12G5  54 ± 5^(c) 9.19 ± 0.19 3  89 ± 2^(c) 9.65 ± 0.17 4   90 ± 1^(c) 9.31 ± 0.16 4 The experiments were performed on membranes from HEK293T cells transiently expressing CXCR4. Data were shown as means ± S.E.M. The number of experiments is given as n. ^(a)No significant displacement at 0.5 μM. ^(b)Maximum not reached at the highest test concentration of 0.5 μM, displacement at 0.5 μM. ^(c)Significantly different from 100%.

Example 1.7 Inhibition of CXCR4-Mediated Signal Transduction

In an effort to functionally characterize the Nanobodies 238D2 and 238D4, we measured their ability to activate G-protein signaling or to inhibit the CXCL12-induced G-protein signaling in HEK293T cells transiently co-transfected with cDNAs encoding CXCR4 and Gα_(qi5). This assay is based upon the use of the chimeric Gα_(qi5)-protein that contains a Gα_(q) backbone with the 5 C-terminal amino acids replaced by those from Gα_(i). The chimeric G-protein is activated by CXCR4 like a Gα_(i) subunit but transduces signals like Gα_(q) proteins (Coward, P., et al., Chimeric G Proteins Allow a High-Throughput Signaling Assay of G1-Coupled Receptors, Analytical Biochemistry (1999) 270: 242-248). Thus, the activation of Gα_(qi5) can be quantified by the measurement of accumulated inositol phosphates. CXCL12 stimulates inositol phosphate accumulation with a pEC₅₀ of 7.89±0.21 (n=4). No agonist activity was observed for the Nanobodies 238D2 or 238D4 up to a concentration of 100 nM. However, 238D2 and 238D4 fully inhibited the CXCL12-induced accumulation of inositol phosphates in a concentration-dependent manner (FIG. 5A).

In addition, we investigated the ability of the Nanobodies 238D2 and 238D4 to inhibit the CXCL12-induced activation at a later step of signal transduction in HEK293T cells transiently transfected with pcDNA3.1-CXCR4 and a β-galactosidase reporter gene under the control of a cAMP response element (CRE). Stimulation of G_(i)-protein-coupled receptors like CXCR4 may result in an inhibition the forskolin-induced activation of CRE. Indeed, CXCL12 potently inhibited the forskolin (3 μM)-induced activation of the CRE-dependent transcription of β-galactosidase with a pEC₅₀ of 9.78±0.09 (n=11), whereas the Nanobodies 238D2 and 238D4 did not show any agonist activity in the absence of CXCL12 (FIG. 5B). However, both nanobodies inhibited the CXCL12 response by parallel rightward-shifts of the concentration response curves of CXCL12 without affecting its maximal effect upon increasing Nanobody concentrations. Schild analysis showed linearity between log(CR−1) and −log [Nanobody] (M) with slopes of 0.91±0.20 and 0.71±0.17 (not significantly different from unity) for both 238D2 and 238D4, respectively (FIG. 5B). These results indicate competitive antagonism of the CXCL12-induced activation of signal transduction for both Nanobodies. Based on the Schild plot data, pK_(B) values of 7.64±0.16 and 7.70±0.16 were calculated for 238D2 and 238D4, respectively.

In order to demonstrate the specificity of the Nanobodies for CXCR4, we also investigated the effects of 238D2 and 238D4 on other chemokine and non-chemokine receptor signaling by using the CRE/β-galactosidase reporter gene. Sub-maximally effective agonist concentrations (50-80% E_(max)) in the absence or the presence of 3 μM forskolin were used to stimulate the cells. The Nanobodies 238D2 and 238D4 even in concentrations up to 2.5 μM did not alter the agonist-induced inhibition of the forskolin (3 μM)-induced activation of CRE in HEK293T cells transiently transfected with cDNA encoding CXCR1, CXCR2, CXCR3, CXCR6, CCR5, CCR7 or histamine H4 receptors, respectively (FIG. 7). Furthermore, 238D2 and 238D4 (2.5 μM) did not inhibit the activation of endogenously expressed β₂-adrenoceptors by the β₂-adrenoceptor agonist salbutamol (100 nM). These results demonstrate an over 100-fold selectivity of 238D2 and 238D4 for CXCR4 over all other receptors tested.

The chemoattractant or anti-chemoattractant effects of CXCL12 and the Nanobodies were investigated in Jurkat leukaemia T cells endogenously expressing CXCR4. CXCL12 induced migration of Jurkat cells with a typical bell-shaped profile with a pEC₅₀ of 9.41±0.26 (n=5) for the first phase of the concentration response curve. 238D2 and 238D4 were unable to induce any significant migration of Jurkat cells by themselves (FIG. 5C). In contrast, both 238D2 and 238D4 concentration-dependently inhibited the migration of Jurkat cells towards 300 pM CXCL12 (FIG. 5C).

TABLE B-4 Maximal inhibition (I_(max)) and functional inhibitory potency (pK_(i) or pIC₅₀) of the Nanobodies 238D2 and 238D4. 238D2 238D4 I_(max) (%) pK_(i) or pIC₅₀ n I_(max) (%) pK_(i) or pIC₅₀ n IP accumulation HEK293T-CXCR4-Gα_(qi5)/30 nM  86 ± 12 8.51 ± 0.11 4 90 ± 5 8.39 ± 0.24 4 CXCL12 CRE activation HEK293T-CXCR4-CREbgal/  104 ± 5^(a)  7.64 ± 0.16^(b) 4   90 ± 15^(a)  7.70 ± 0.16^(b) 6 0.01-100 nM CXCL12 Chemotaxis Jurkat/0.3 nM CXCL12 106 ± 2 8.33 ± 0.16 4 101 ± 4  8.31 ± 0.22 4 Anti-HIV-1 activity (in nM) MT-4/NL4.3 30.7 40.3 MT-4/HE 26.7 82.0 PBMC/NL4.3 30.9 13.7 PBMC/HE 44.7 13.6 PBMC/BaL >100 >100 U87.CD4.CXCR4/NL4.3 44.7 107 U87.CD4.CCR5/BaL >500 (no activity) >500 (no activity) Data were shown as means ± S.E.M. The number of experiments is given as n.

Example 1.8 HIV-1 Activity

The ability of 238D2 and 238D4 to block the entry of the X4 HIV-1 strain NL4.3, the R5HIV-1 strain BaL and the dual-tropic (R5/X4) HIV-1 strain HE was investigated on endogenously CXCR4 expressing MT-4 cells, endogenously CXCR4 and CCR5 expressing PBMCs or U87.CD4 cells stably transfected with CCR5 or CXCR4, respectively. Control experiments with the small molecule antagonists for CXCR4 (AMD3100) and CCR5 (maraviroc) were simultaneously performed. Additional control experiments in the absence of any virus confirm that the Nanobodies show no toxicity at the highest test concentrations (500 nM in MT-4 and U87.CD4 cells; 100 nM in PBMCs). 238D2 and 238D4 were equipotently active against the CXCR4-using strains NL4.3 and HE in both MT-4 cells and PBMCs in nanomolar concentrations (Table B-4). Furthermore, both Nanobodies were active against NL4.3 in U87 cells expressing recombinant CD4 and CXCR4. However, 238D2 and 238D4 failed to inhibit the entry and infectivity of the CCR5-using HIV-1 particles into PBMCs and U87.CD4.CCR5 cells. For comparison, maraviroc was potently active against BaL on PBMCs (IC₅₀=3.13 nM) and U87.CD4.CCR5 cells (IC₅₀=0.72 nM) in control experiments. The activity of the Nanobodies against X4-HIV-1 and failure to inhibit R5 viruses show that their anti-retroviral activity is directly linked to their interaction with CXCR4.

Example 2 Generation of Nanobodies Directed Against Human CXCR7

The same approach as for Nanobodies directed against human CXCR4 is used. In particular, the method uses at least the following steps:

-   a) Immunization with whole living cell (e.g. HEK293) overexpressing     human CXCR7; -   b) Immunization and selection using different cell types (e.g.     HEK293 for immunization, CHO-membrane enriched for human CXCR7 for     1^(st) round selection, COS7 membranes enriched for human CXCR7 for     2^(nd) round selection); -   c) Optionally, washing with mild buffer, e.g. PBS (without     detergents).

Reference is also made to the human protein sequence of CXCR7 that can e.g. be found in the Swissprot database under “P25106”.

Example 3 Examples of HIV In Vitro Neutralization Assays Example 3.1 Single-Round Pseudovirus Neutralization Assay

Reference is made to James M. Binley, Terri Wrin, Bette Korber, Michael B. Zwick, Meng Wang, Colombe Chappey, Gabriela Stiegler, Renate Kunert, Susan Zolla-Pazner, Hermann Katinger, Christos J. Petropoulos, and Dennis R. Burton (Comprehensive Cross-Clade Neutralization Analysis of a Panel of Anti-Human Immunodeficiency Virus Type 1 Monoclonal Antibodies. Journal of Virology, December 2004, p. 13232-13252, Vol. 78, No. 23).

A recombinant-virus assay involving a single round of virus infection is used to measure neutralization. Recombinant luciferase pseudoviruses are incubated for 1 h at 37° C. with 10 serial fourfold dilutions of MAbs or heat-inactivated plasma, usually starting from 50 μg/ml (MAbs) or a 1:20 dilution (plasma). In a variant protocol, virus is incubated with antibody for 18 h before the mixture is added to target cells. U87 cells expressing CD4 plus the CCR5 and CXCR4 coreceptors are inoculated with virus-antibody (Ab) dilutions in the absence of added cations. Virus stocks are screened to ensure that they were functional and yielded a high luciferase reporter light signal in target cell lysates. Input virus used in each experiment is not standardized. Virus infectivity is determined 72 h postinoculation by measuring the amount of luciferase activity expressed in infected cells. Neutralizing activity is reported as the concentration or dilution of each MAb or plasma required to confer 50% (IC₅₀) or 90% (IC₉₀) inhibition of infection (percent inhibition={1−[luciferase Ab/luciferase−Ab]}×100). To eliminate nonspecific neutralization, the criterion for genuine neutralization is that the titer must be at least 2.5-fold higher against HIV-1 than it is against the amphotropic control MuLV. Due to the large size of this study, each individual virus-Ab combination is in general tested only once. To ensure that the results are reproducible, the control viruses JR-CSF (R5-tropic) and NL4-3 (X4-tropic) are run at least six times in all assays. The reproducibility of the assay within and between runs is assessed by looking at these controls.

Example 3.2 GHOST Assay

Reference is made to Steyaert et al. (2007, Inhibition of replication of primary HIV-1 isolates in huPBL-NOD/Scid mice by antibodies from HIV-1 infected patients. Antiviral Res. 2007 August; 75(2):129-38. Epub 2007 Mar. 6). Human plasma and purified immunoglobulins are screened for neutralizing activity with a highly sensitive GHOST cell-based assay (Dormers et al., 2003).

These cells are derived from human osteosarcoma cells and are transfected with the gene coding for human CD4, one of the HIV co-receptors (CCR5 or CXCR4) and green fluorescent protein under the control of the HIV-2 LTR promoter. The number of infected cells is measured by FACS. Plasma samples are diluted 1/20 and purified IgGs to a concentration of 500 ug/ml. The format of the neutralization assay is 24/24/48 where 24/x/x is the time in hours during which antibody and virus are pre-incubated, x/24/x is the time in hours during which cells are exposed to these mixtures and x/x/48 is the time in hours between the start of viral inoculation and the FACS analysis. The percentage neutralization is calculated as 100−[(# infected cells of tested sample/# infected cells of seronegative control)×100].

Example 3.4 PBMC Assay

Reference is made to Beirnaert et al., 2000.

Virus neutralization assays are carried out as described previously with some minor modifications. Briefly, culture supernatant of virus infected PBMCs (50 TCID50/well) and twofold serial dilutions (1/10-1/1,280) of heat-inactivated serum (30 min at 56° C.) are mixed in a 96-well tray and incubated for 1 hr at 37° C. in a 5% CO2 atmosphere. In each experiment, an HIV (−) serum is assayed in the same conditions as the sample sera, to serve as a negative control. Subsequently, 7.5×104/well PHAstimulated, IL-2 maintained PBMCs are added. After 2 hr incubation, the cells are washed three times and incubated in RPMI 1640 medium supplemented with 20 U/ml IL-2, 15% FCS, 0.03% L-Glutamine, 2 mg/ml polybrene, 5 mg/ml hydrocortisone and antibiotics. For every neutralization experiment, the virus is titrated again to compare the infectivity of the virus stock in different donor PBMCs. If the virus titer differed from the input virus titer by more than a factor 3, the neutralization experiment is considered invalid. Viral replication is assessed after 7 days using a non-commercial antigen capture ELISA that captures antigen of HIV-1 belonging to Group M as well as to Group O [Beirnaert et al., 1998, Identification and characterization of sera from HIV-infected individuals with broad cross-neutralizing activity against group M (env clade A-H) and group O primary HIV-1 isolates. J Med Virol. 2000 September; 62(1):14-24]. Fifty-percent inhibitory doses (ID50) are defined as the reciprocal of the highest serum dilution that produced 50% reduction in absorbance value in the antigen capture assay compared to the negative serum control. Serum neutralizing titers of <1/10 are considered negative. Sera are assayed in duplicate and tests are carried out at least three times.

Example 3.5 HIV In Vivo Neutralization Models Example 3.5.1 Hu-PBL (NOD/SCID)

Reference in made to: Gauduin, M. C., Parren, P. W., Weir, R., Barbas, C. F., Burton, D. R., Koup, R. A. (1997. Passive immunization with a human monoclonal antibody protects hu-PBL-SCID mice against challenge by primary isolates of HIV-1. Nat. Med. 3, 1389-4393, Steyaert et al., 2007).

To assess virus-inhibiting activity in vivo, human polyclonal immunoglobulins are administered to huPBL-NOD/Scid mice 6 days after reconstitution and 1 day before viral challenge. All injections are given intraperitoneally (i.p.). Each experimental group may consist of four mice. The minimal viral inoculum needed to infect all mice is determined in preliminary titrations. The chimeric mice that survived the graft-versus-host reaction (82%) are sacrificed 14 days after challenge and viral load is measured in their plasma using COBAS Amplicor HIV-1 Monitor™ version 1.5 (Roche) according manufacturer's instructions. Due to the limited availability of mouse plasma, these may be diluted 1/100 and therefore the lower limit of detection of this assay is about 3.70 log equiv/ml.

Example 3.5.2 SHIV Macaque Model

For antibody infusions, vaginal challenge, and blood and mucosal collections, macaques are lightly anesthetized with ketamine HCl. A SHIV89.9PD challenge stock is grown and titrated in rhesus PBMC. Antibodies are infused intravenously 24 h prior to virus challenge. Vaginal SHIV challenge is done by gently introducing 1 ml of a 1:5 dilution of virus stock (600 TCID50) into the vaginal canal of macaques using a 1-ml syringe. Macaques are kept in a prone position for at least 15 min postchallenge. Thirty days prior to vaginal challenge, macaques may have received 30 mg of medroxyprogesterone acetate (Depo-Provera, Upjohn, Kalamazoo, Mich.) by intramuscular injection. Recent titration experiments in progesterone treated macaques demonstrated that the monkeys are exposed to 10-50 animal

infectious doses of SHIV89.6PD. After vaginal challenge, monkeys are followed clinically and by routine hematology, lymphocyte subset, and blood chemistry measurements. Inguinal lymph node biopsies for viral co-culture and PCR for viral DNA are done on all monkeys at 3 weeks post-virus challenge.

Example 4 Optimization of the Functional Nanobody Profile Directed Against hCXCR4

In order to improve the functional inhibitory profile by engineering, a series of bivalent Nanobodies on the basis of 238D2 and 238D4 were generated (Table B-5).

TABLE B-5 Sequences of selected bivalent Nanobodies Amino Acid Sequence Clone name SEQ ID NO: EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGL 238D2-10GS-238D2 261 EWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPED TAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSSGGGGSGGGGSEVQ LVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGLEWV SGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPEDTAV YYCAKSRVSRTGLYTYDNRGQGTQVTVSS EVQLMESGGGLVQAGGSLRLSCAASGRTFNNYAMGWFRRAPGKER 238D4-20GS-238D4 262 EFVAAITRSGVRSGVSAIYGDSVKDRFTISRDNAKNTLYLQMNSL KPEDTAVYTCAASAIGSGALRRFEYDYSGQGTQVTVSSGGGGSGG GGSGGGGSGGGGSEVQLMESGGGLVQAGGSLRLSCAASGRTFNNY AMGWFRRAPGKEREFVAAITRSGVRSGVSAIYGDSVKDRFTISRD NAKNTLYLQMNSLKPEDTAVYTCAASAIGSGALRRFEYDYSGQGT QVTVSS EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGL 238D2-15GS-238D4 263 EWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPED TAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSSGGGGSGGGGSGGG GSEVQLMESGGGLVQAGGSLRLSCAASGRTFNNYAMGWFRRAPGK EREFVAAITRSGVRSGVSAIYGDSVKDRFTISRDNAKNTLYLQMN SLKPEDTAVYTCAASAIGSGALRRFEYDYSGQGTQVTVSS EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGL 238D2-20GS-238D4 264 EWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPED TAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSSGGGGSGGGGSGGG GSGGGGSEVQLMESGGGLVQAGGSLRLSCAASGRTFNNYAMGWFR RAPGKEREFVAAITRSGVRSGVSAIYGDSVKDRFTISRDNAKNTL YLQMNSLKPEDTAVYTCAASAIGSGALRRFEYDYSGQGTQVTVSS EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGL 238D2-20GS-238C5 265 EWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPED TAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSSGGGGSGGGGSGGG GSGGGGSEVQLMESGGGLVQAGGSLRLACAASGFTFEDYAIGWFR KAPGKEREGVSCISGSDGSTTYADSVKGRFTISTDNAKNTVYLEM NSLKPEDTAVYYCAQQYGVGGRVVCPGPYEYDVWGQGTQVTVSS EVQLVESGGGLVQTGGSLRLSCAASGFTFSSYAMSWVRQAPGKGL 238D2-20GS-238B10 266 EWVSGIKSSGDSTRYAGSVKGRFTISRDNAKNMLYLQMYSLKPED TAVYYCAKSRVSRTGLYTYDNRGQGTQVTVSSGGGGSGGGGSGGG GSGGGGSEVQLVESGGGFVQAGGSLRLSCETSGRPLLGYTIAWFR QVPGKEREFVAYHRWSDGANLYADSVKGRFTISGHNAKNTVSLQM NSLKPEDTAVYYCAAARMTTSNDKEYLYWGQGTQVTVSS

Recombinant linking of 238D2 to 238D2 and 238D4 to 238D4 using amino acid linkers with repetitive GGGGS sequences of different sizes resulted in a 14 and 4.4-fold increase in affinity to CXCR4, respectively (Table B-6, Table B-7). A significant increase in apparent affinity was also observed when 238D2 was linked to 238D4. In case of the obtained heterobivalent Nanobody 238D2-20GS-238D4, the affinity to CXCR4 was increased by 27 and 17-fold over the respective monovalent counterparts 238D2 and 238D4. Alteration in the linker size between 15 amino acids and 20 amino acids did not show any influence in respect to the receptor affinity. However, linking of 238D2 to the inactive Nanobody 238B10 or to the low affinity Nanobody 238C5 did not result in an increase but even lowered the receptor affinity. These results exclude the possibility that the linker increases the receptor affinity by its own. Furthermore, competition in binding between 238D2 and 238D4 (FIGS. 4B,4C) and lacking increase of [¹²⁵I]-CXCL12 displacement potency by equi-molar mixing of 238D2 and 238D4 argues against a positive cooperative effect due to allosteric binding on the same receptor molecule.

TABLE B-6 Receptor affinity (pK_(i)), relative potency and maximal displacement of [¹²⁵I]-CXCL12 by bivalent Nanobodies in comparison to their monovalent counterparts. The experiments were performed on membranes from HEK293T cells transiently expressing CXCR4. Data are shown as means ± S.E.M. The number of experiments is given as n. Displacem. (%) pK_(i) Rel. potency n 238D2-10GS-238D2 95 ± 5 9.16 ± 0.08 14^(a)    3 238D4-20GS-238D4 96 ± 5 8.85 ± 0.08 4.4^(b)  4 238D2-15GS-238D4 92 ± 6 9.45 ± 0.09 28^(a)/17^(b) 3 238D2-20GS-238D4 103 ± 4  9.44 ± 0.07 27^(a)/17^(b) 3 238D2-20GS-238C5 110 ± 2  7.35 ± 0.07 0.18^(a) 2 238D2-20GS-238B10  43 ± 11^(c) <7.00 <0.1^(a)  2 238D2 + 238D4 (1:1)  92 ± 11 8.00 ± 0.36 1.0^(a)/0.6^(b) 3 ^(a)Potency relative to those of monovalent 238D2. ^(b)Potency relative to those of monovalent 238D4. ^(c)Maximum not reached at the highest test concentration of 0.5 μM, displacement at 0.5 μM.

TABLE B-7 Chemotaxis - Maximal inhibition (I_(max)) and functional inhibitory potency (pK_(i) or pIC₅₀) of the compound 238D2-15GS-238D4 and compound 238D2-20GS-238D4. 238D2-15GS-238D4 238D2-20GS-238D4 I_(max) (%) pK_(i) or pIC₅₀ n I_(max) (%) pK_(i) or pIC₅₀ n Chemotaxis Jurkat/0.3 nM CXCL12 107 ± 5 9.86 ± 0.04 3 100 ± 4 10.19 ± 0.27 3 Anti-HIV-1 activity (in nM) MT-4/NL4.3 0.25 0.25 MT-4/HE 0.16 010 PBMC/NL4.3 0.5 0.2 PBMC/HE 1.5 2.3 PBMC/BaL >100 >100 U87.CD4.CXCR4/NL4.3 0.36 0.35 U87.CD4.CCR5/BaL >100 >100 Data are shown as means ± S.E.M. The number of experiments is given as n.

The most potent bivalent Nanobodies 238D2-15GS-238D4 and 238D2-20GS-238D4 were further functionally characterized. Both, 238D2-15GS-238D4 and 238D2-20GS-238D4 fully antagonized the chemoattractant effects of CXCL12 in subnanomolar concentrations (pK_(i)=9.86±0.04 and 10.19±0.27, respectively; n=3). Furthermore, 238D2-15GS-238D4 and 238D2-20GS-238D4 inhibited the entry of the X4 HIV-1 strain NL4.3 into MT-4, PBMCs and stably CD4 and CXCR4 expressing U87 cells in subnanomolar concentrations (IC50: 0.2-0.5 nM). Both Nanobodies also potently inhibit the entry of the dual-tropic HIV-1 strain HE into MT-4 cells, endogenously expressing CXCR4 but not CCR5. The bivalent Nanobodies were somewhat less potent in the inhibition of HIV-1 HE into PBMCs which endogenously express CCR5 in addition to CXCR4 and thus can partially circumvent a blocking of CXCR4. Indeed, the lack of anti-retroviral efficiency in control experiments with the CCR5-using HIV-1 strain BaL confirms that the anti-retroviral activity of the bivalent Nanobodies 238D2-15GS-238D4 and 238D2-20GS-238D4 is dependent on CXCR4 as co-receptor for virus entry (Table B-7). In conclusion, linking of the Nanobodies 238D2 and 238D4 to a single chain molecule result in a significant increase of anti-chemotactic and anti-retroviral potency via blocking of CXCR4 by even one to two orders of magnitude (see Table B-7 but also Table B-4; FIG. 8).

Example 5 HIV-1 Infection Assays

The anti-HIV-1 potencies of Nanobodies on the X4 HIV-1 clone NL4.3 or primary virus strains UG270 (X4, Clade D), CI#17 (X4, clade B), the R5 HIV-1 strain BaL or the R5/X4 HIV-1 HE strain in MT-4, U87.CD4.CXCR4, U87.CD4.CCR5 and/or phytohemagglutin-stimulated PBMCs from different donors were determined by measuring the cytopathic effect of HIV-1 (in MT-4 and U87 cell lines) microscopically and by tetrazolium-based colorimetric evaluation or by quantification of the viral p24 antigen production in the culture supernatant (PBMCs) as described in detail. Primary virus strains were grown 1 or 2 times in PBMC only.

The CXCR4-using (X4) HIV-1 clone NL4.3 was obtained from the National Institutes of Health NIAID AIDS Reagent program (Bethesda, Md.), the CCR5-using (R5) HIV-1 strain BaL was obtained from the Medical Research. Council AIDS reagent project (Herts, UK). The dual-tropic (R5/X4) HIV-1 HE strain was initially isolated from a patient at the University Hospital in Leuven.

The MT-4 cells were seeded out in 96-well plate and the U87 cells in 24-well plates. The test compounds were added at different concentrations together with HIV-1 and the plates were maintained at 37° C. in 10% CO₂. Cytopathic effect induced by the virus was monitored by daily microscopic evaluation of the virus-infected cell cultures. At day 4-5 after infection, when strong cytopathic effect was observed in the positive control (i.e., untreated HIV-infected cells), the cell viability was assessed via the in situ reduction of the tetrazolium compound MTS, using the CeliTiter 96® AQ_(ueous) One Solution Cell Proliferation Assay (Promega, Madison, Wis.). The absorbance was then measured spectrophotometrically at 490 nm with a 96-well plate reader (Molecular Devices, Sunnyvale, Calif.) and compared with four cell control replicates (cells without virus and drugs) and four virus control wells (virus-infected cells without drugs). The 50% inhibitory concentration (IC₅₀, i.e. the drug concentration that inhibits HIV-induced cell death by 50%), was calculated for each compound from the dose-response curve. The CC₅₀ or 50% cytotoxic concentration of each of the compounds was determined from the reduction of viability of uninfected cells exposed to the agents, as measured by the MTS method described above.

Peripheral blood mononuclear cells (PBMCs) from healthy donors were isolated by density centrifugation (Lymphoprep; Nycomed Pharina, AS Diagnostics, Oslo, Norway) and stimulated with phytohemagglutin for 3 days. The activated cells were washed with PBS and viral infections were performed as described previously (Schols D, et al. (1997) Inhibition of T-tropic HIV strains by selective antagonization of the chemokine receptor CXCR4. J Exp Med 186:1383-1388). At 8-10 days after the start of the infection, viral p24 Ag was detected in the culture supernatant by an enzyme-linked immunosorbent assay (Perkin Elmer, Brussels, Belgium).

TABLE B-7 Inhibition by Nanobodies 238D2, 238D4 and biparatopics of infection of PBMC by primary virus isolates PBMC + PBMC + PBMC + PBMC + PBMC + PBMC + PBMC + PBMC + MT-4/NL4.3 NL4.3 NL4.3 BaL BaL UG270 UG270 CI#17 CI#17 exp. 1 donor 1 donor 2 donor 1 donor 2 donor 1 donor 2 donor 1 donor 2 238D2 IC50 (ng/ml) 701.4 468.4 307.4 >1000 >1000 492.5 447.2 >1000 >1000 IC90 (ng/ml) 849 >1000 >1000 >1000 >1000 >1000 851.3 >1000 >1000 238D4 IC50 (ng/ml) 832.9 >1000 551.1 >1000 >1000 >1000 >1000 >1000 >1000 IC90 (ng/ml) >1000 >1000 >1000 >1000 >1000 >1000 >1000 >1000 >1000 238D2-20GS- IC50 (ng/ml) 6.9 18.2 9.2 >1000 >1000 24.2 83.1 100.9 120 238D4 IC90 (ng/ml) 23.8 97.2 73.1 >1000 >1000 139.1 167.8 468.1 654.0 238D2-15GS- IC50 (ng/ml) 16.6 10 17.9 >1000 >1000 21.2 89.4 28.5 35.5 238D4 IC90 (ng/ml) 71.1 109.5 34.1 >1000 >1000 78.9 170.3 196.5 607.6 AMD3100 IC50 (ng/ml) 6.4 1.1 >40 nd nd 3.6 17.9 12.1 14.9 IC90 (ng/ml) >40 9.9 >40 nd nd 15.4 34.1 >40 37.9 maraviroc IC50 (ng/ml) nd nd nd 1.5 0.8 nd nd nd nd IC90 (ng/ml) nd nd nd 27.3 13.1 nd nd nd nd PBMC from donor 1 to 2 nM IC50 nM IC50 NL4.3 238D2 31.23 20.49 238D4 >67 36.74 238D2-15GS-238D4 0.33 0.60 238D2-20GS-238D4 0.61 0.31 UG270 238D2 32.83 29.81 238D4 >67 >67 238D2-15GS-238D4 0.71 2.98 238D2-20GS-238D4 0.81 2.77 CI#17 238D2 >67 >67 238D4 >67 >67 238D2-15GS-238D4 0.95 1.18 238D2-20GS-238D4 3.36 4.00 BAL 238D2 >67 >67 238D4 >67 >67 238D2-15GS-238D4 >67 >67 238D2-20GS-238D4 >67 >67

Example 6 Nanobodies Against CD4 Example 6.1 Animal Immunizations

Llama 58, 59 and 60 were immunized according to standard protocols with 6 boosts, each of them with approximately 10⁸ of human peripheral blood lymphocytes (hPBLs). Blood was collected 39 and 43 days after boost 1. In addition, approximately 1 g of lymph node was collected from both animals 39 days after boost 1.

Exampple 6.2 Library Construction

Peripheral blood mononuclear cells were prepared from blood samples using neon-Hypaque according to the manufacturer's instructions. Next, total RNA was extracted from these cells and lymph node tissue, if available, and used as starting material for RT-PCR to amplify Nanobody encoding gene fragments. These fragments were cloned into a phagemid vector. Phage was prepared according to standard methods (see for example the prior art and applications filed by applicant cited herein).

Example 6.3 Selections of Phage Displaying CD4 Binding Nanobodies

Phage libraries 58, 59 and 60 were used for selections on recombinant human CD4 (ImmunoDiagnostics, Inc., cat#7001, lot #5S30/1.5). rhCD4 was immobilized directly on Maxisorp 96 well microtiter plates (Nunc) at 10 ug/ml, 0.1 ug/ml and 0 ug/ml (control). Following incubation with the phage libraries and extensive washing, bound phage was eluted with 100 mM triethylamine (TEA). The eluted phage were amplified and applied in a similar second round of selection. After elution with TEA the second round obtained phage were again amplified and applied into a similar third round selection in which following incubation with the phage and extensive washing, bound phage was aspecifically eluted with TEA, or specifically with 250 nM of gp120 HIV-1 IIIB (Immunodiagnostic).

Individual colonies obtained from the eluted phage pools were grown and i) induced for new phage production and ii) induced with IPTG for Nanobody expression and extraction (periplasmic extracts) according to standard methods (see for example the prior art and applications filed by applicant cited herein).

Example 6.4 Screening for CD4 Binding Nanobodies

In order to determine binding specificity to CD4, the selected clones were tested in an ELISA binding assay setup, using the monoclonal phage pools. Shortly, 1 ug/ml receptor recombinant human CD4 (ImmuneDiagnostics, Inc., cat#7001, lot #5S30/1.5) was immobilized on Maxisorp ELISA plates (Nunc) and free binding sites were blocked using 4% Marvel skimmed milk in PBS. Next, 15 ul of supernatant from the monoclonal phage inductions of the different clones in 100 ul 1% Marvel PBS were allowed to bind to the immobilized antigen. After incubation and a wash step, phage binding was revealed using a HRP-conjugated monoclonal-anti-M13 antibody (Gentaur Cat#27942101). Binding specificity was determined based on OD values compared to controls having received no phage or an irrelevant phage.

FIG. 9 shows a selection of clones binding to CD4.

Example 6.5 Screening for Nanobodies Blocking CD4-gp120 Interaction

Clones tested positive in the CD4 binding assay were screened for their ability to block gp120 binding to CD4. The monovalent his-tagged Nanobodies were purified from periplasmic extracts by affinity and desalting chromatography and used in an ELISA-based competition setup. In short, 1 ug/ml of gp120 HIV-1 IIIB (Immunodiagnostic) was captured by 20 ug/ml of sheep anti-gp120 antibody D7324 (Aalto Bio Reagents) previously coated in 96 well. Maxisorp microtiter plates (Nunc) and blocked with 1% casein in PBS. In parallel, 0.5 ug/ml of biotinylated CD4 was incubated with 500 nM of the different purified Nanobodies in 100 ul 0.1% Casein/PBS. After 1 hour, the biotinylated CD4-Nanobody pre-mixes were incubated 1 hour with the captured gp120. Bound biotinylated CD4 was detected using HRP-conjugated Extravidin (Sigma E2886).

A blocking mouse anti-CD4 monoclonal antibody (Diaclone, clone B-A1 cat#854.030.000) was used as positive control. Blocking activity was determined as loss of OD signal, as compared to wells where no Nanobody was added.

FIG. 10 shows results of this blocking assay using a selection of clones binding to rh CD4. These results indicates that Nanobodies 03F11 and 01B6 are potential blockers for the in vitro interaction of CD4 with gp120.

Example 6.6 Binding of Selected Nanobodies to Jurkat-CD4 Expressing Cells

To check whether the selected Nanobodies recognize cell-surface-native form of CD4, a Flow cytometry experiment was performed where the Nanobodies were tested for specific binding to Jurkat cell expressing CD4.

Periplamsic fractions diluted 2.5 or 5 fold were allowed to bind to 10^(x5) cells of Jurkat cells for 30 minutes at 4° C. in a final volume of 100 ul of 10% FBS (Invitrogen, Cat 10270-106, Lot41G4117OK) in PBS (Invitrogen #14190). Bound Nanobodies were detected with mouse anti-myc antibody (Serotec, Cat#MCA2200, Lot#0407) followed by goat anti-mouse-PE antibody (Jackson #115-115-164. Lot#79725). Dead cells percentage population was determined by staining the cells with TOPRO3 (Molecular probes T3605; Lot #413969).

Using a BD FACSArray Bioanalyzer system, a PE filter 585/42 and a Topro filter 661/16, twenty thousand events were acquired. First a P1 population which represents more than 80% of the total population was selected. From this population the TOPRO3+ cells (dead cells) were excluded. For the P1/TPORO3— population the MCF (mean channel fluorescence) was calculated. Expression of CD4 in Jurkat cells was confirmed by using 10 ug/ml of an anti-CD4 monoclonal antibody (Diaclone, clone B-A1 cat#854.030.000). Staining of the cells with an irrelevant Nanobody 0306, anti myc and/or the goat anti mouse-PE antibodies antibody was performed as negative controls.

The results obtained for the different Nanobodies and control antibodies are shown in FIG. 11. These data showed only clear binding of 03F11 to CD4 positive Jurkat.

Example 6.7 Inhibition by the CD4 Binding Nanobody 03F11 of Infection of MT4 Cells by NL4.3 Virus

In a first experiment the 03F11, 01E2, 01H12 and 01B6 were tested for anti-HIV activity using the NL4.3 strain on MT4 cells. To demonstrated replication p24 levels were determined. Of the four Nanobodies tested only 03F11 showed strong inhibitory activity (IC50=15 nM) while the other 3 showed no anti-HIV activity even at 500 nM. In a second experiment again using MT4 cell and the NL4.3 virus strain but now using the MTS method to detect HIV replication, again only 03F11 inhibited infection of cells by NL4.3 was observed (IC50=85 nM). Again no inhibition was observed with the other 3 Nanobodies even when used at 500 nM.

TABLE C Non-exhaustive list of some therapeutically relevant Targets of  the invention (and desired action of an amino acid sequence, a Nanobody or a polypeptide of the invention). Target of invention Amino Acid Sequence SEQ ID NO: hCD4 MNRGVPFRHLLLVLQLALLPAATQGKHVVLGKKGDTVELTCTASQKKSIQ 268 FHWKNSNQIKILGNQGSFLTNGPSKLNDRADSRRSLWDQGNFPLIIKNLK IEDSDTYICEVEDQKEEVQLLVFGLTANSDTHLLQGQSLTLTLESPPGSS PSVQCRSPRGKNIQGGKTLSVSQLELQDSGTWTCTVLQNQKKVEFKIDIV VLAFQKASSIVYKKEGEQVEFSFPLAFTVEKLTGSGELWWQAFRASSSKS WITFDLKNKEVSVKRVTQDPKLQMGKKLPLHLTLPQALPQYAGSGNLTLA LEAKTGKLHQEVNLVVMRATQLQKNLTCEVWGPTSPKLMLSLKLENKEAK VSKREKAVWVLNPEAGMWQCLLSDSGQVLLESNIKVLPTWSTPVQPMALI VLGGVAGLLLFIGLGIFFCVRCRHRRRQAERMSQIKRELSEKKTCQCPHR FQKTCSPI hCXCR4 MEGISSIPLPLLQIYTSDNYTEEMGSGDYDSMKEPCFREENANFNKIFLP 254 TIYSIIFLTGIVGNGLVILVMGYQKKLRSMTDKYRLHLSVADLLFVITLP FWAVDAVANWYFGNFLCKAVHVIYTVNLYSSVLILAFISLDRYLAIVHAT NSQRPRKLLAEKVVYVGVWIPALLLTIPDFIFANVSEADDRYICDRFYPN DLWVVVFQFQHIMVGLILPGIVILSCYCIIISKLSHSKGHQKRKALKTTV ILILAFFACWLPYYIGISIDSFILLEIIKQGCEFENTVHKWISITEALAF FHCCLNPILYAFLGAKFKTSAQHALTSVSRGSSLKILSKGKRGGHSSVST ESESSSFHSS hCCR5 MDYQVSSPIYDINYYTSEPCQKINVKQIAARLLPPLYSLVFIFGFVGNML 269 VILILINCKRLKSMTDIYLLNLAISDLFFLLTVPFWAHYAAAQWDFGNTM CQLLTGLYFIGFFSGIFFIILLTIDRYLAVVHRVFALKARTVTFGVVTSV ITWVVAVFASLPGIIFTRSQKEGLHYTCSSHFPYSQYQFWKNFQTLKIVI LGLVLPLLVMVICYSGILKTLLRCRNEKKRHRAVRLIFTIMIVYFLFWAP YNIVLLLNTFQEFFGLNNCSSSNRLDQAMQVTETLGMTHCCINPIIYAFV GEKFRNYLLVFFQKHIAKRFCKCCSIFQQEAPERASSVYTRSTGEQEISV GL hTLR4 MELNFYKIPDNLPFSTKNLDLSFNPLRHLGSYSFFSFPELQVLDLSRCEI 270 QTIEDGAYQSLSHLSTLILTGNPIQSLALGAFSGLSSLQKLVAVETNLAS LENFPIGHLKTLKELNVAHNLIQSFKLPEYFSNLTNLEHLDLSSNKIQSI YCTDLRVLHQMPLLNLSLDLSLNPMNFIQPGAFKEIRLHKLTLRNNFDSL NVMKTCIQGLAGLEVHRLVEGEFRNEGNLEKFDKSALEGLCNLTIEEFRL AYLDYYLDDIIDLFNCLTNVSSFSLVSVTIERVKDFSYNFGWQHLELVNC KFGQFPTLKLKSLKRLTFTSNKGGNAFSEVDLPSLEFLDLSRNGLSFKGC CSQSDFGTTSLKYLDLSFNGVITMSSNFLGLEQLEHLDFQHSNLKQMSEF SVFLSLRNLIYLDISHTHTRVAFNGIFNGLSSLEVEKMAGNSFQENFLPD IFTELRNLTFLDLSQCQLEQLSPTAFNSLSSLQVLNMSHNNFFSLDTFPY KCLNSLQVLDYSLNHIMTSKKQELQHFPSSLAFLNETQNDFACTCEHQSF LQWIKDQRQLLVEVERMECATPSDKQCMPVLSLNITCQMNKTIIGVSVLS VLVVSVVAVLVYKFYFHLMLLAGCIKYGRGENIYDAFVIYSSQDEDWVRN ELVKNLEEGVPPFQLCLHYRDFIPGVAIAANIIHEGFEKSRKVIVVVSQH FIQSRWCIFEYEIAQTWQFLSSRAGIIFIVLQKVEKTLLRQQVELYRLLS RNTYLEWEDSVLGRHIFWRRLRKALLDGKSWNPEGTVGTGCNWQEATSI human MAFPPRRRLRLGPRGLPLLLSGLLEPLCRAFNLDVDSPAEYSGPEGSYFG 271 alphaV FAVDFFVPSASSRMFLLVGAPKANTTQPGIVEGGQVLKCDWSSTRRCQPI integrin EFDATGNRDYAKDDPLEFKSHQWFGASVRSKQDKILACAPLYHWRTEMKQ EREPVGTCFLQDGTKTVEYAPCRSQDIDADGQGFCQGGFSIDFTKADRVL LGGPGSFYWQGQLISDQVAETVSKYDPNVYSIKYNNQLATRTAQAIFDDS YLGYSVAVGDFNGDGIDDFVSGVPRAARTLGMVYIYDGKNMSSLYNFTGE QMAAYFGFSVAATDINGDDYADVFIGAPLFMDRGSDGKLQEVGQVSVSLQ RASGDFQTTKLNGFEVFARFGSAIAPLGDLDQDGFNDIAIAAPYGGEDKK GIVYIFNGRSTGLNAVPSQILEGQWAARSMPPSFGYSMKGATDIDKNGYP DLIVGAFGVDRAILYRARPVITVNAGLEVYPSILNQDNKTCSLPGTALKV SCFNVRFCLKADGKGVLPRKLNFQVELLLDKLKQKGAIRRALFLYSRSPS HSKNMTISRGGLMQCEELIAYLRDESEFRDKLTPITIFMEYRLDYRTAAD TTGLQPILNQFTPANISRQAHILLDCGEDNVCKPKLEVSVDSDQKKIYIG DDNPLTLIVKAQNQGEGAYEAELIVSIPLQADFIGVVRNNEALARLSCAF KTENQTRQVVCDLGNPMKAGTQLLAGLRFSVHQQSEMDTSVEFDLQIQSS NLFDKVSPVVSHKVDLAVLAAVEIRGVSSPDHIFLPIPNWEHKENPETEE DVGPVVQHIYELRNNGPSSFSKAMLHLQWPYKYNNNTLLYILHYDIDGPM NCTSDMEINPLRIKISSLQTTEKNDTVAGQGERDHLITKRDLALSEGDIH TLGCGVAQCLKTVCQVGRLDRGKSAILYVKSLLWTETFMNKENQNHSYSL KSSASFNVIEFPYKNLPIEDITNSTLVTTNVTWGIQPAPMPVPVWVIILA VLAGLLLLAVLVFVMYRMGFFKRVRPPQEEQEREQLQPHENGEGNSET human MRARPRPRPLWATVLALGALAGVGVGGPNICTTRGVSSCQQCLAVSPMCA 272 beta3 WCSDEALPLGSPRCDLKENLLKDNCAPESIEFPVSEARVLEDRPLSDKGS integrin GDSSQVTQVSPQRIALRLRPDDSKNFSIQVRQVEDYPVDIYYLMDLSYSM KDDLWSIQNLGTKLATQMRKLTSNLRIGFGAFVDKPVSPYMYISPPEALE NPCYDMKTTCLPMFGYKHVLTLTDQVTRFNEEVKKQSVSRNRDAPEGGFD AIMQATVCDEKIGWRNDASHLLVFTTDAKTHIALDGRLAGIVQPNDGQCH VGSDNHYSASTTMDYPSLGLMTEKLSQKNINLIFAVTENVVNLYQNYSEL IPGTTVGVLSMDSSNVLQLIVDAYGKIRSHVELEVRDLPEELSLSFNATC LNNEVIPGLKSCMGLKIGDTVSFSIEAKVRGCPQEKEKSFTIKPVGFKDS LIVQVTFDCDCACQAQAEPNSHRCNNGNGTFECGVCRCGPGWLGSQCECS EEDYRPSQQDECSPREGQPVCSQRGECLCGQCVCHSSDFGKITGKYCECD DFSCVRYKGEMCSGHGQCSCGDCLCDSDWTGYYCNCTTRTDTCMSSNGLL CSGRGKCECGSCVCIQPGSYGDTCEKCPTCPDACTFKKECVECKKFDRGA LHDENTCNRYCRDEIESVKELKDTGKDAVNCTYKNEDDCVVRFQYYEDSS GKSILYVVEEPECPKGPDILVVLLSVMGAILLIGLAALLIWKLLITIHDR KEFAKFEEERARAKWDTANNPLYKEATSTFTNITYRGT human MNLQPIFWIGLISSVCCVFAQTDENRCLKANAKSCGECTQAGPNCGWCTN 273 beta1 STFLQEGMPTSARCDDLEALKKKGCPPDDIENPRGSKDIKKNKNVTNRSK integrin GTAEKLKPEDITQIQPQQLVLRLRSGEPQTFTLKFKRAEDYPIDLYYLMD LSYSMKDDLENVKSLGTDLMNEMRRITSDFRIGFGSFVEKTVMPYISTTP AKLRNPVTSEQNCTSPFSYKNVLSLTNKGEVFNELVGKQRISGNLDSPEG GFDAIMQVAVCGSLIGWRNVTRLLVFSTDAGFHFAGDGKLGGIVLPNDGQ CHLENNMYTMSHYYDYPSIAHLVQKLSENNIQTIFAVTEEFQPVYKELKN LIPKSRVGTLSANSSNVIQLIIDAYNSLSSEVILENGKLSEGVTISYKSY CKNGVNGTGENGRECSNISIGDEVQFEISITSNKCPKKDEDSFKIRPLGF TEEVEVILQYICECECQSEGIPESPKCHEGNGTFECGACRCNEGRVGRHC ECSTDEVNSEDMDAYORKENSSEICSNNGECVCGQCVCRKRDNTNEIYSG KFCECDNFNCDRSNGLICGCNGVCKCRVCECNPNYTGSACDCSLDTSTCE ASNGQICNGRGICECGVCKCTDPKFQGQTCEMCQTCLGVCAEHKECVQCR AFNKGEKKDTCTQECSYFNITKVESRDKLPQPVQPDPVSHCKEKDVDDCW FYFTYSVNGNNEVMVHVVENPECPTGPDIIPIVAGVVAGIVLIGLALLLI WKLLMIIHDRREFAKFEKEKMNAKWDTGENPIYKSAVTTVVNPKYEGK human MGPERTGAAPLPLLLVLALSQGILNCCLAYNVGLPEAKIFSGPSSEQFGY 274 alpha2 AVQQFINPKGNWLLVGSPWSGFPENRMGDVYKCPVDLSTATCEKLNLQTS integrin TSIPNVTEMKTNMSLGLILTRNMGTGGFLTCGPLWAQQCGNQYYTTGVCS DISPDFQLSASFSPATQPCPSLIDVVVVCDESNSIYPWDAVKNFLEKFVQ GLDIGPTKTQVGLIQYANNPRVVFNLNTYKTKEEMIVATSQTSQYGGDLT NTFGAIQYARKYAYSAASGGRRSATKVMVVVTDGESHDGSMLKAVIDQCN HDNILRFGIAVLGYLNRNALDTKNLIKEIKAIASIPTERYFFNVSDEAAL LEKAGTLGEQIFSIEGTVQGGDNFQMEMSQVGFSADYSSQNDILMLGAVG AFGWSGTIVQKTSHGHLIFPKQAFDQILQRNHSSYLGYSVAAITSTGEST HFVAGAPRANYTGQIVLYSVNENGNITVIQAHRGDQIGSYFGSVLCSVDV DKDTITDVLLVGAPMYMSDLKKEEGRVYLFTIKEGILGQHQFLEGPEGIE NTRFGSAIAALSDINMDGFNDVIVGSPLENQNSGAVYIYNGHQGTIRTKY SQKILGSDGAFRSHLQYFGRSLDGYGDLNGDSITDVSIGAFGQVVQLWSQ SIADVAIEASFTPEKITLVNKNAQIILKLCFSAKFRPTKQNNQVAIVYNI TLDADGFSSRVTSRGLFKENNERCLQKNMVVNQAQSCPEHIIYIQEPSDV VNSLDLRVDISLENPGTSPALEAYSETAKVFSIPFHKDCGEDGLCISDLV LDVRQIPAAQEQPFIVSNQNKRLTFSVTLKNKRESAYNTGIVVDFSENLF FASFSLPVDGTEVTCQVAASQKSVACDVGYPALKREQQVTFTINFDFNLQ NLQNQASLSFQALSESQEENKADNLVNLKIPLLYDAEIHLTRSTNINFYE ISSDGNVPSIVHSFEDVGPKFIFSLKVTTGSVPVSMATVIIHIPQYTKEK NPLMYLTGVQTDKAGDISCNADINPLKIGQTSSSVSFKSENFRHTKELNC RTASCSNVTCWLKDVHMKGEYFVNVTTRIWNGTFASSTFQTVQLTAAAEI NTYNPEIYVIEDNTVTIPLMIMKPDEKATVPTGVIIGSIIAGILLLLALV AILWKLGFFKRKYEKMTKNPDEIDETTELSS hCD81 MGVEGCTKCIKYLLFVFNFVFWLAGGVILGVALWLRHDPQTTNLLYLELG 275 DKPAPNTFYVGIYILIAVGAVMMFVGFLGCYGAIQESQCLLGTFFTCLVI LFACEVAAGIWGFVNKDQIAKDVKQFYDQALQQAVVDDDANNAKAVVKTF HETLDCCGSSTLTALTTSVLKNNLCPSGSNIISNLFKEDCHQKIDDLFSG KLYLIGIAATVVAVIMIFEMILSMVLCCGIRNSSVY hSR-BI MGCSAKARWAAGALGVAGLLCAVLGAVMIVMVPSLIKQQVLKNVRIDPSS 276 LSFNMWKEIPIPFYLSVYFFDVMNPSEILKGEKPQVRERGPYVYREFRHK SNITFNNNDTVSFLEYRTFQFQPSKSHGSESDYIVMPNILVLGAAVMMEN KPMTLKLIMTLAFTTLGERAFMNRTVGEIMWGYKDPLVNLINKYFPGMFP FKDKFGLFAELNNSDSGLFTVFTGVQNISRIHLVDKWNGLSKVDFWHSDQ CNMINGTSGQMWPPFMTPESSLEFYSPEACRSMKLMYKESGVFEGIPTYR FVAPKTLFANGSIYPPNEGFCPCLESGIQNVSTCRFSAPLFLSHPHFLNA DPVLAEAVTGLHPNQEAHSLFLDIHPVTGIPMNCSVKLQLSLYMKSVAGI GQTGKIEPVVLPLLWFAESGAMEGETLHTFYTQLVLMPKVMHYAQYVLLA LGCVLLLVPVICQIRSQEKCYLFWSSSKKGSKDKEAIQAYSESLMTSAPK GSVLQEAKL hClaudin- MANAGLQLLGFILAFLGWIGAIVSTALPQWRIYSYAGDNIVTAQRMYEGL 277 1 WMSCVSQSTGQIQCKVFDSLLNLSSTLQATRALMVVGILLGVIAIFVATV DMKCMKCLEDDEVQKMRMAVIGGAIFLLAGLAILVATAWYGNRIVQEFYD PMTPVNARYEFGQALFTGWAAASLCLLGGALLCCSCPRKTTSYPTPRPYP KPAPSSGKDYV hClaudin- MASAGMQILGVVLTLLGWVNGLVSCALPMWKVTAFIGNSIVVAQVVWEGL 278 6 WMSCVVQSTGQMQCKVYDSLLALPQDLQAARALCVIALLVALFGLLVYLA GAKCTTCVEEKDSKARLVLTSGIVFVISGVLTLIPVCWTAHAIIRDFYNP LVAEAQKRELGASLYLGWAASGLLLLGGGLLCCTCPSGGSQGPSHYMARY STSAPAISRGPSEYPTKNYV hClaudin- MASTGLELLGMTLAVLGWLGTLVSCALPLWKVTAFIGNSIVVAQVVWEGL 279 9 WMSCVVQSTGQMQCKVYDSLLALPQDLQAARALCVIALLLALLGLLVAIT GAQCTTCVEDEGAKARIVLTAGVILLLAGILVLIPVCWTAHAIIQDFYNP LVAEALKRELGASLYLGWAAAALLMLGGGLLCCTCPPPQVERPRGPRLGY SIPSRSGASGLDKRDYV

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following aspects.

All references disclosed herein are incorporated by reference in their entirety for the purpose and information indicated in the specification. 

1. Polypeptide comprising one or more Nanobodies that specifically bind one of the Targets of the invention and that inhibit viral entry.
 2. Polypeptide according to claim 1, wherein the IC50 in the HIV-1 infection assays is equal or below 100 nM, preferably 50 nM, more preferably 10 nM, even more preferably 1 nM.
 3. Polypeptide according to claim 1, that has an antiviral activity, expressed as IC50 measured in the HIV-1 infection assay, equal or below 100 nM, preferably 50 nM, more preferably 10 nM, even more preferably 1 nM.
 4. Polypeptide according to claim 1, wherein the one or more Nanobodies specifically binds one of the Targets of the invention selected from the group consisting of hCD4, hCXCR4, hCCR5, hTLR4, human alphaV integrin, human beta3 integrin, human beta1 integrin, human alpha2 integrin, hCD81, hSR-BI, hClaudin-1, hClaudin-6 and hClaudin-9.
 5. Polypeptide according to claim 1, that specifically binds to one of the Targets of the invention selected from the group consisting of amino acid sequences with SEQ IDs: 254, 268 to
 279. 6. Polypeptide according to claim 1, that specifically binds to hCXCR4 (SEQ ID NO: 254).
 7. Polypeptide according to claim 1, that specifically binds to hCD4 (SEQ ID NO: 268).
 8. Polypeptide of claim 1, that comprises two or more Nanobodies.
 9. Polypeptide of claim 8, that comprises two Nanobodies.
 10. Polypeptide of claim 1, wherein at least one Nanobody essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is chosen from the group consisting of: a) the amino acid sequences of SEQ ID NO's: 142 to 143; b) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 142 to 143; c) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 142 to 143; and/or CDR2 is chosen from the group consisting of: d) the amino acid sequences of SEQ ID NO's: 174 to 175; e) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 174 to 175; f) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 174 to 175; and/or CDR3 is chosen from the group consisting of: g) the amino acid sequences of SEQ ID NO's: 206 to 207; h) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 206 to 207; i) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 206 to
 207. 11. Polypeptide of claim 1, wherein two Nanobodies essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is chosen from the group consisting of: a) the amino acid sequences of SEQ ID NO's: 142 to 143; b) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 142 to 143; c) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 142 to 143; and/or CDR2 is chosen from the group consisting of: d) the amino acid sequences of SEQ ID NO's: 174 to 175; e) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 174 to 175; f) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 174 to 175; and/or CDR3 is chosen from the group consisting of: g) the amino acid sequences of SEQ ID NO's: 206 to 207; h) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 206 to 207; i) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 206 to
 207. 12. Polypeptide of claim 1, wherein one Nanobody essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is chosen from the group consisting of: a) the amino acid sequences of SEQ ID NO: 142; b) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO: 142; c) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO: 142; and CDR2 is chosen from the group consisting of: d) the amino acid sequences of SEQ ID NO: 174; e) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO: 174; f) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO: 174; and CDR3 is chosen from the group consisting of: g) the amino acid sequences of SEQ ID NO: 206; h) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO: 206; i) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO: 206; wherein another Nanobody essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which—CDR1 is chosen from the group consisting of: j) the amino acid sequences of SEQ ID NO's SEQ ID NO: 143; k) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO: 143; l) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO: 143; and CDR2 is chosen from the group consisting of: m) the amino acid sequences of SEQ ID NO: 175; n) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO: 175; o) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO: 175; and CDR3 is chosen from the group consisting of: p) the amino acid sequences of SEQ ID NO: 207; q) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO: 207; r) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO:
 207. 13. Polypeptide of claim 1, wherein the Nanobodies are selected from the group consisting of Nanobodies having at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's 238 to
 239. 14. Polypeptide of claim 1, wherein the polypeptide is selected from the group consisting of polypeptides having at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's 261 to
 264. 15. Nanobody that essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is chosen from the group consisting of: a) the amino acid sequences of SEQ ID NO's: 142 to 143; b) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 142 to 143; c) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 142 to 143; and CDR2 is chosen from the group consisting of: d) the amino acid sequences of SEQ ID NO's: 174 to 175; e) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 174 to 175; f) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 174 to 175; and CDR3 is chosen from the group consisting of: g) the amino acid sequences of SEQ ID NO's: 206 to 207; h) amino acid sequences that have at least 80% amino acid identity with at least one of the amino acid sequences of SEQ ID NO's: 206 to 207; i) amino acid sequences that have 3, 2, or 1 amino acid difference with at least one of the amino acid sequences of SEQ ID NO's: 206 to
 207. 16. Polypeptide of claim 1, wherein at least one Nanobody essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is chosen from the group consisting of: a) the amino acid sequence of SEQ ID NO: 287; b) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 287; c) amino acid sequences that have 3, 2, or 1 amino acid difference with the amino acid sequence of SEQ ID NO: 287; and/or CDR2 is chosen from the group consisting of: d) the amino acid sequence of SEQ ID NO: 295; e) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 295; f) amino acid sequences that have 3, 2, or 1 amino acid difference with at least the amino acid sequence of SEQ ID NO: 295; and/or CDR3 is chosen from the group consisting of: g) the amino acid sequence of SEQ ID NO: 303; h) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 303; i) amino acid sequences that have 3, 2, or 1 amino acid difference with at least the amino acid sequence of SEQ ID NO:
 303. 17. Polypeptide of claim 1, wherein two Nanobodies essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is chosen from the group consisting of: a) the amino acid sequence of SEQ ID NO: 287; b) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 287; c) amino acid sequences that have 3, 2, or 1 amino acid difference with at least the amino acid sequence of SEQ ID NO: 287; and/or CDR2 is chosen from the group consisting of: d) the amino acid sequence of SEQ ID NO: 295; e) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 295; f) amino acid sequences that have 3, 2, or 1 amino acid difference with at least the amino acid sequence of SEQ ID NO: 295; and/or CDR3 is chosen from the group consisting of: g) the amino acid sequence of SEQ ID NO: 303; h) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 303; i) amino acid sequences that have 3, 2, or 1 amino acid difference with at least the amino acid sequence of SEQ ID NO:
 303. 18. Polypeptide of claim 1, wherein the Nanobodies are selected from the group consisting of Nanobodies having at least 80% amino acid identity with SEQ ID NO:
 311. 19. Nanobody that essentially consists of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is chosen from the group consisting of: a) the amino acid sequence of SEQ ID NO: 287; b) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 287; c) amino acid sequences that have 3, 2, or 1 amino acid difference with at least the amino acid sequence of SEQ ID NO: 287; and CDR2 is chosen from the group consisting of: d) the amino acid sequence of SEQ ID NO: 291; e) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 291; f) amino acid sequences that have 3, 2, or 1 amino acid difference with at least the amino acid sequence of SEQ ID NO: 291; and CDR3 is chosen from the group consisting of: g) the amino acid sequence of SEQ ID NO: 303; h) amino acid sequences that have at least 80% amino acid identity with at least the amino acid sequence of SEQ ID NO: 303; i) amino acid sequences that have 3, 2, or 1 amino acid difference with at least the amino acid sequence of SEQ ID NO:
 303. 20. Nucleic acid or nucleotide sequence, that encodes a polypeptide of claim
 1. 21. Host cell that under suitable circumstances is capable of expressing, a polypeptide of claim
 1. 22. Pharmaceutical composition comprising a polypeptide of claim
 1. 23. Pharmaceutical composition according to claim 22 that further comprises at least one pharmaceutically acceptable carrier, diluent or excipient and/or adjuvant, and that optionally comprises one or more further pharmaceutically active polypeptides and/or compounds.
 24. Method for screening amino acid sequences directed against human CXCR4 (SEQ ID NO: 254) that comprises at least the steps of: a) providing a set, collection or library of nucleic acid sequences encoding amino acid sequences; b) screening said set, collection or library of nucleic acid sequences for nucleic acid sequences that encode an amino acid sequence that can bind to and/or has affinity for a Target of the invention such as e.g. human CXCR4 or hCD4 and that is cross-blocked or is cross blocking a polypeptide according to claim 1; and c) isolating said nucleic acid sequence, followed by expressing said amino acid sequence.
 25. Method/use for treatment of viral and/or bacterial induced disease or disorder, said method/use comprising administering, to a subject in need thereof, a pharmaceutically active amount of at least one polypeptide of claim
 1. 